Fix gif not animating problem.

Runtime/flow/raster_cache.cs

                 return false;
             }
 
+            foreach (DrawCmd drawCmd in picture.drawCmds) {
+                switch (drawCmd) {
+                    case DrawImage cmd: {
+                        if (cmd.image.isDynamic)
+                            return false;
+                        break;
+                    }
+                    case DrawImageNine cmd: {
+                        if (cmd.image.isDynamic)
+                            return false;
+                        break;
+                    }
+                    case DrawImageRect cmd: {
+                        if (cmd.image.isDynamic)
+                            return false;
+                        break;
+                    }
+                }
+            }
+
             return true;
         }
 

Runtime/ui/painting/codec_gif.cs

             if (this._texture == null) {
                 this._texture = new Texture2D(this._width, this._height, TextureFormat.BGRA32, false);
                 this._texture.hideFlags = HideFlags.HideAndDontSave;
-                this._image = new Image(this._texture);
+                this._image = new Image(this._texture, isDynamic: true);
                 this._frameData.frameInfo.image = this._image;
             }
             this._frameData.gifFrame = this._decoder.currentFrame;

Runtime/ui/painting/image.cs

         Texture _texture;
         readonly bool _noDispose;
         readonly bool _isAsset;
+        readonly bool _isDynamic;
-        public Image(Texture texture, bool noDispose = false, bool isAsset = false, AssetBundle bundle = null) {
+        public Image(Texture texture, bool noDispose = false, bool isAsset = false, AssetBundle bundle = null, bool isDynamic = false) {
             D.assert(!noDispose || !isAsset && bundle == null);
             D.assert(isAsset || bundle == null);
 
             this._bundle = bundle;
+            this._isDynamic = isDynamic;
         }
 
         public int width {
 
         public Texture texture {
             get { return this._texture; }
+        }
+
+        public bool isDynamic {
+            get { return this._isDynamic;  }
         }
 
         ~Image() {