[1.5.4] Upgrade app and app_bar.

Runtime/material/app.cs

                 this._navigatorObservers.Add(this._heroController);
             }
             else {
-                this._navigatorObservers = null;
+                this._navigatorObservers = new List<NavigatorObserver>();
             }
         }
 

Runtime/material/app_bar.cs

             Widget flexibleSpace = null,
             PreferredSizeWidget bottom = null,
             float? elevation = null,
+            ShapeBorder shape = null,
+            IconThemeData actionsIconTheme = null,
             TextTheme textTheme = null,
             bool primary = true,
             bool? centerTitle = null,
             this.flexibleSpace = flexibleSpace;
             this.bottom = bottom;
             this.elevation = elevation;
+            this.shape = shape;
+            this.actionsIconTheme = actionsIconTheme;
             this.textTheme = textTheme;
             this.primary = primary;
             this.centerTitle = centerTitle;
 
         public readonly float? elevation;
 
+        public readonly ShapeBorder shape;
+
+
+        public readonly IconThemeData actionsIconTheme;
 
         public readonly TextTheme textTheme;
 
             bool canPop = parentRoute?.canPop ?? false;
             bool useCloseButton = parentRoute is PageRoute && ((PageRoute) parentRoute).fullscreenDialog;
 
-            IconThemeData appBarIconTheme = this.widget.iconTheme
+            IconThemeData overallIconTheme = this.widget.iconTheme
+            IconThemeData actionsIconTheme = this.widget.actionsIconTheme
+                                             ?? appBarTheme.actionsIconTheme
+                                             ?? overallIconTheme;
             TextStyle centerStyle = this.widget.textTheme?.title
                                     ?? appBarTheme.textTheme?.title
                                     ?? themeData.primaryTextTheme.title;
                     sideStyle = sideStyle.copyWith(color: sideStyle.color.withOpacity(opacity));
                 }
 
-                appBarIconTheme = appBarIconTheme.copyWith(
-                    opacity: opacity * (appBarIconTheme.opacity ?? 1.0f)
+                overallIconTheme = overallIconTheme.copyWith(
+                    opacity: opacity * (overallIconTheme.opacity ?? 1.0f)
+                );
+                actionsIconTheme = actionsIconTheme.copyWith(
+                    opacity: opacity * (actionsIconTheme.opacity ?? 1.0f)
                 );
             }
 
                     tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip);
             }
 
+            if (actions != null) {
+                actions = IconTheme.merge(
+                    data: actionsIconTheme,
+                    child: actions
+                );
+            }
+
             Widget toolbar = new NavigationToolbar(
                 leading: leading,
                 middle: title,
                 child: new CustomSingleChildLayout(
                     layoutDelegate: new _ToolbarContainerLayout(),
                     child: IconTheme.merge(
-                        data: appBarIconTheme,
+                        data: overallIconTheme,
                         child: new DefaultTextStyle(
                             style: sideStyle,
                             child: toolbar)
                     elevation: this.widget.elevation
                                ?? appBarTheme.elevation
                                ?? _defaultElevation,
+                    shape: this.widget.shape,
                     child: appBar
                 ));
         }
             Color backgroundColor,
             Brightness? brightness,
             IconThemeData iconTheme,
+            IconThemeData actionsIconTheme,
             TextTheme textTheme,
             bool primary,
             bool? centerTitle,
             this.backgroundColor = backgroundColor;
             this.brightness = brightness;
             this.iconTheme = iconTheme;
+            this.actionsIconTheme = actionsIconTheme;
             this.textTheme = textTheme;
             this.primary = primary;
             this.centerTitle = centerTitle;
         public readonly Color backgroundColor;
         public readonly Brightness? brightness;
         public readonly IconThemeData iconTheme;
+        public readonly IconThemeData actionsIconTheme;
         public readonly TextTheme textTheme;
         public readonly bool primary;
         public readonly bool? centerTitle;
                    || this.backgroundColor != oldDelegate.backgroundColor
                    || this.brightness != oldDelegate.brightness
                    || this.iconTheme != oldDelegate.iconTheme
+                   || this.actionsIconTheme != oldDelegate.actionsIconTheme
                    || this.textTheme != oldDelegate.textTheme
                    || this.primary != oldDelegate.primary
                    || this.centerTitle != oldDelegate.centerTitle
             Color backgroundColor = null,
             Brightness? brightness = null,
             IconThemeData iconTheme = null,
+            IconThemeData actionsIconTheme = null,
             TextTheme textTheme = null,
             bool primary = true,
             bool? centerTitle = null,
             this.backgroundColor = backgroundColor;
             this.brightness = brightness;
             this.iconTheme = iconTheme;
+            this.actionsIconTheme = actionsIconTheme;
             this.textTheme = textTheme;
             this.primary = primary;
             this.centerTitle = centerTitle;
         public readonly Brightness? brightness;
 
         public readonly IconThemeData iconTheme;
+        
+        public readonly IconThemeData actionsIconTheme;
 
         public readonly TextTheme textTheme;
 
                         backgroundColor: this.widget.backgroundColor,
                         brightness: this.widget.brightness,
                         iconTheme: this.widget.iconTheme,
+                        actionsIconTheme: this.widget.actionsIconTheme,
                         textTheme: this.widget.textTheme,
                         primary: this.widget.primary,
                         centerTitle: this.widget.centerTitle,

Runtime/material/app_bar_theme.cs

             Color color = null,
             float? elevation = null,
             IconThemeData iconTheme = null,
+            IconThemeData actionsIconTheme = null,
             TextTheme textTheme = null
         ) {
             this.brightness = brightness;
+            this.actionsIconTheme = actionsIconTheme;
             this.textTheme = textTheme;
         }
 
 
         public readonly IconThemeData iconTheme;
 
+        public readonly IconThemeData actionsIconTheme;
+
         public readonly TextTheme textTheme;
 
         AppBarTheme copyWith(
             IconThemeData iconTheme = null,
+            IconThemeData actionsIconTheme = null,
             TextTheme textTheme = null
         ) {
             return new AppBarTheme(
                 iconTheme: iconTheme ?? this.iconTheme,
+                actionsIconTheme: actionsIconTheme ?? this.actionsIconTheme,
                 textTheme: textTheme ?? this.textTheme
             );
         }
                 color: Color.lerp(a?.color, b?.color, t),
                 elevation: MathUtils.lerpFloat(a?.elevation ?? 0.0f, b?.elevation ?? 0.0f, t),
                 iconTheme: IconThemeData.lerp(a?.iconTheme, b?.iconTheme, t),
+                actionsIconTheme: IconThemeData.lerp(a?.actionsIconTheme, b?.actionsIconTheme, t),
                 textTheme: TextTheme.lerp(a?.textTheme, b?.textTheme, t)
             );
         }
             hashCode = (hashCode * 397) ^ this.color?.GetHashCode() ?? 0;
             hashCode = (hashCode * 397) ^ this.elevation?.GetHashCode() ?? 0;
             hashCode = (hashCode * 397) ^ this.iconTheme?.GetHashCode() ?? 0;
+            hashCode = (hashCode * 397) ^ this.actionsIconTheme?.GetHashCode() ?? 0;
             hashCode = (hashCode * 397) ^ this.textTheme?.GetHashCode() ?? 0;
             return hashCode;
         }
                    && other.color == this.color
                    && other.elevation == this.elevation
                    && other.iconTheme == this.iconTheme
+                   && other.actionsIconTheme == this.actionsIconTheme
                    && other.textTheme == this.textTheme;
         }
 
             properties.add(new DiagnosticsProperty<Color>("color", this.color, defaultValue: null));
             properties.add(new DiagnosticsProperty<float?>("elevation", this.elevation, defaultValue: null));
             properties.add(new DiagnosticsProperty<IconThemeData>("iconTheme", this.iconTheme, defaultValue: null));
+            properties.add(new DiagnosticsProperty<IconThemeData>("actionsIconTheme", this.actionsIconTheme, defaultValue: null));
             properties.add(new DiagnosticsProperty<TextTheme>("textTheme", this.textTheme, defaultValue: null));
         }
     }