Merge branch 'shiyun/skia' of https://github.com/Unity-Technologies/com.unity.uiwidgets into shiyun/skia

com.unity.uiwidgets/Runtime/cupertino/app.cs

             Dictionary<LogicalKeySet, Intent> shortcuts = null,
             Dictionary<LocalKey, ActionFactory> actions = null
         ) : base(key: key) {
-            D.assert(routes != null);
-            D.assert(navigatorObservers != null);
-            D.assert(showPerformanceOverlay != null);
-            D.assert(checkerboardRasterCacheImages != null);
-            D.assert(checkerboardOffscreenLayers != null);
-            D.assert(showSemanticsDebugger != null);
-            D.assert(debugShowCheckedModeBanner != null);
 
             supportedLocales = supportedLocales ?? new List<Locale> {new Locale("en", "US")};
             this.navigatorKey = navigatorKey;

com.unity.uiwidgets/Runtime/foundation/binding.cs

             Timeline.finishSync();
         }
 
-        static bool _debugInitialized = false;
+        bool _debugInitialized = false;
 
         public Window window => Window.instance;
 

com.unity.uiwidgets/Runtime/gestures/mouse_tracking.cs

             MouseDetectorAnnotationFinder annotationFinder
             
         ) {
-            D.assert(_router != null);
+            D.assert(router != null);
             D.assert(annotationFinder != null);
             _router = router;
             router.addGlobalRoute(_handleEvent);
             if (Event is PointerSignalEvent)
                 return;
             int device = Event.device;
-            _MouseState existingState = _mouseStates[device];
+            _MouseState existingState = _mouseStates.getOrDefault(device);
             if (!_shouldMarkStateDirty(existingState, Event))
                 return;
             PointerEvent previousEvent = existingState?.latestEvent;
             
             _MouseState targetState = null;
             if (targetEvent != null) {
-              targetState = _mouseStates[targetEvent.device];
+              targetState = _mouseStates.getOrDefault(targetEvent.device);
               if (targetState == null) {
                 targetState = new  _MouseState(initialEvent: targetEvent);
                 _mouseStates[targetState.device] = targetState;

com.unity.uiwidgets/Runtime/widgets/basic.cs

             this.softWrap = softWrap;
             this.overflow = overflow;
             this.textScaleFactor = textScaleFactor;
-            this.maxLines = maxLines ?? 0;
+            this.maxLines = maxLines;
             this.locale = locale;
             this.strutStyle = strutStyle;
             this.textWidthBasis = textWidthBasis;
         public readonly  bool softWrap;
         public readonly  TextOverflow overflow;
         public readonly  float textScaleFactor;
-        public readonly  int maxLines;
+        public readonly  int? maxLines;
         public readonly  Locale locale;
         public readonly  StrutStyle strutStyle;
         public readonly  TextWidthBasis textWidthBasis;

com.unity.uiwidgets/Runtime/widgets/binding.cs

     }
 
     public class WidgetsBinding : RendererBinding {
-        public static WidgetsBinding instance {
-            get { return _instance; }
+        public new static WidgetsBinding instance {
+            get { return (WidgetsBinding) RendererBinding.instance; }
-        static WidgetsBinding _instance;
 
         protected override void initInstances() {
             base.initInstances();
             get { return _buildOwner; }
         }
 
-        BuildOwner _buildOwner = new BuildOwner();
+        BuildOwner _buildOwner;
 
         public FocusManager focusManager {
             get { return _buildOwner.focusManager; }
     public class UiWidgetsBinding : WidgetsBinding {
         // todo 
         public static WidgetsBinding ensureInitialized() {
-            if (WidgetsBinding.instance == null)
-                new UiWidgetsBinding();
+            if (WidgetsBinding.instance == null) {
+                return new UiWidgetsBinding();
+            }
+            
             return WidgetsBinding.instance;
         }
     }

com.unity.uiwidgets/Runtime/widgets/framework.cs

 
         public T dependOnInheritedWidgetOfExactType<T>(object aspect = null) where T : InheritedWidget {
             D.assert(_debugCheckStateIsActiveForAncestorLookup());
-            InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[typeof(T)];
+            InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets.getOrDefault(typeof(T));
             
             if (ancestor != null) {
                 D.assert(ancestor is InheritedElement);

com.unity.uiwidgets/Runtime/widgets/text.cs

         public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
             base.debugFillProperties(properties);
             style?.debugFillProperties(properties);
-            properties.add(new EnumProperty<TextAlign>("textAlign", textAlign.Value, defaultValue: null));
+            properties.add(new EnumProperty<TextAlign?>("textAlign", textAlign, defaultValue: null));
             properties.add(new FlagProperty("softWrap", value: softWrap, ifTrue: "wrapping at box width", ifFalse: "no wrapping except at line break characters", showName: true));
             properties.add(new EnumProperty<TextOverflow>("overflow", overflow, defaultValue: null));
             properties.add(new IntProperty("maxLines", maxLines, defaultValue: null));