fix runtime debug assertion code: this assertion will only be called if the debug mode is enabled

README-ZH.md

 
 在编辑器菜单栏选择```UIWidgets->EnableDebug```
 
-如果想在runtime开启debug模式，请在项目代码中设置```UIWidgetsGlobalConfiguration.EnableDebugAtRuntime = true```。在默认情况下debug模式为关闭状态。
-
 ## 使用Window Scope保护外部调用
 如果您在调试时遇到 `AssertionError: Window.instance is null` 或者在调用 `Window.instance` 时得到空指针, 那么您需要
 使用以下方式来保护您的调用，使之可以在正确的Isolate上执行回调逻辑：

README.md

 
 ## Debug UIWidgets Application
 
-In Unity editor, you can switch debug/release mode by “UIWidgets->EnableDebug”.
-
-You can also enable debug mode in runtime by setting ```UIWidgetsGlobalConfiguration.EnableDebugAtRuntime = true``` in your project. Note that this value is set to false by default.
+You can switch debug/release mode by “UIWidgets->EnableDebug” in the Unity Editor.
 
 ## Using Window Scope
 If you see the error `AssertionError: Window.instance is null` or null pointer error of `Window.instance`,

com.unity.uiwidgets/Runtime/engine/UIWidgetsGlobalConfiguration.cs

 
         //disable incremental gc by default
         public static bool EnableIncrementalGC = false;
-        
-        //disable debug at runtime by default
-        public static bool EnableDebugAtRuntime = false;
     }
 }

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

 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using Unity.UIWidgets.engine;
 
         public static bool debugPrintMouseHoverEvents = false;
 
+        public const string debugScriptingDefineSymbol = "DebugUIWidgets";
+
         public static HSVColor debugCurrentRepaintColor =
             HSVColor.fromAHSV(0.4f, 60.0f, 1.0f, 1.0f);
 
             Debug.LogException(new AssertionError(message: message, innerException: ex));
         }
 
-        [Conditional("UNITY_ASSERTIONS")]
+        [Conditional(debugScriptingDefineSymbol)]
-        [Conditional("UNITY_ASSERTIONS")]
+        
+        [Conditional(debugScriptingDefineSymbol)]
         public static void assert(bool result, Func<string> message = null) {
             if ( enableDebug && !result ) {
                 throw new AssertionError(message != null ? message() : "");
 #if UNITY_EDITOR
         static bool? _enableDebug = null;
+
+        private static void setRuntimeSymbolsForTarget(BuildTargetGroup targetGroup, bool enabled) {
+            string defines = PlayerSettings.GetScriptingDefineSymbolsForGroup(targetGroup);
+            var defineList = defines.Split(';');
+            var newDefineList = new List<string>();
+            foreach (var define in defineList) {
+                if (define != debugScriptingDefineSymbol) {
+                    newDefineList.Add(define);
+                }
+            }
+
+            if (enabled) {
+                newDefineList.Add(debugScriptingDefineSymbol);
+            }
+            
+            PlayerSettings.SetScriptingDefineSymbolsForGroup(targetGroup, String.Join(";", newDefineList));
+        }
+        
         public static bool enableDebug {
             get {
                 if (_enableDebug == null) {
                 }
                 _enableDebug = value;
                 EditorPrefs.SetInt("UIWidgetsDebug",value ? 1 : 0);
+                setRuntimeSymbolsForTarget(BuildTargetGroup.Android, value);
+                setRuntimeSymbolsForTarget(BuildTargetGroup.iOS, value);
+                setRuntimeSymbolsForTarget(BuildTargetGroup.Standalone, value);
-        public static bool enableDebug => UIWidgetsGlobalConfiguration.EnableDebugAtRuntime;
+        //In runtime, we use the Conditional decorator "debugScriptingDefineSymbol" instead of this to enable/disable debug mode 
+        public static bool enableDebug => true;
 #endif
 
         public static void _debugDrawDoubleRect(Canvas canvas, Rect outerRect, Rect innerRect, Color color) {