Merge pull request #243 from UnityTech/optimizeViewMetricsUpdate

avoid mark viewMetrics dirty in update, which will potentially leads …

Runtime/editor/editor_utils.cs

         public void OnEnable() {
             this._lastDevicePixelRatio = GameViewUtil.getGameViewDevicePixelRatio();
         }
+
+        public void onViewMetricsChanged() {
+            
+        }
         
         public float devicePixelRatio {
             get { return this._lastDevicePixelRatio; }

Runtime/engine/DisplayMetrics.cs

         void OnEnable();
         void OnGUI();
         void Update();
+        void onViewMetricsChanged();
 
         float devicePixelRatio { get; }
 
         }
 
         public void Update() {
+            
+        }
+
+        public void onViewMetricsChanged() {
-
 
         public float devicePixelRatio {
             get {

Runtime/engine/UIWidgetsPanel.cs

 
         void _handleViewMetricsChanged(string method, List<JSONNode> args) {
             this._windowAdapter.onViewMetricsChanged();
-            this._displayMetrics.Update();
+            this._displayMetrics.onViewMetricsChanged();
         }
 
         protected override void OnEnable() {