DevTools: check for canForceCompositingMode before trying to emulate device metrics.

Source/devtools/front_end/OverridesSupport.js

Index: Source/devtools/front_end/OverridesSupport.js
diff --git a/Source/devtools/front_end/OverridesSupport.js b/Source/devtools/front_end/OverridesSupport.js
index b4f5c643f3b61e36a99d54e531a36c10e6c37e0a..60f3d96ef85e33b1008c0b6fa2bddcabe0a96e2b 100644
--- a/Source/devtools/front_end/OverridesSupport.js
+++ b/Source/devtools/front_end/OverridesSupport.js
@@ -29,10 +29,15 @@
  */
 
 /**
+ * @extends {WebInspector.Object}
  * @constructor
  */
 WebInspector.OverridesSupport = function()
 {
+    WebInspector.resourceTreeModel.addEventListener(WebInspector.ResourceTreeModel.EventTypes.MainFrameNavigated, this._updateCanForceCompositingMode.bind(this), this);
+    this.canForceCompositingMode = true;

[pfeldman, 2013/10/31 11:23:58]

Should be private w/ accessor if necessary.

[dgozman, 2013/10/31 12:39:50]

Done.

+    this._updateCanForceCompositingMode();

[pfeldman, 2013/10/31 11:23:58]

It is too early, you should do this if you are about to enable some override.

[dgozman, 2013/10/31 12:39:50]

No, it's needed right away to disable UI elements.

+
     this._updateAllOverrides();
 
     WebInspector.settings.overrideUserAgent.addChangeListener(this._userAgentChanged, this);
@@ -54,6 +59,10 @@ WebInspector.OverridesSupport = function()
     WebInspector.settings.emulatedCSSMedia.addChangeListener(this._cssMediaChanged, this);
 }
 
+WebInspector.OverridesSupport.Events = {
+    CanForceCompositingModeChanged: "CanForceCompositingModeChanged",
+}
+
 /**
  * @constructor
  * @param {number} width
@@ -400,7 +409,8 @@ WebInspector.OverridesSupport.prototype = {
     {
         WebInspector.settings.deviceMetrics.set(deviceMetrics);
         WebInspector.settings.userAgent.set(userAgent);
-        WebInspector.settings.overrideDeviceMetrics.set(true);
+        if (this.canForceCompositingMode)
+            WebInspector.settings.overrideDeviceMetrics.set(true);
         WebInspector.settings.overrideUserAgent.set(true);
         WebInspector.settings.emulateTouchEvents.set(true);
     },
@@ -488,7 +498,23 @@ WebInspector.OverridesSupport.prototype = {
                 WebInspector.settings.showEmulationViewInDrawer.set(true);
             WebInspector.inspectorView.showViewInDrawer("emulation");
         }
-    }
+    },
+
+    _updateCanForceCompositingMode: function()
+    {
+        function callback(error, result)
+        {
+            if (!error) {
+                this.canForceCompositingMode = result;
+                this.dispatchEventToListeners(WebInspector.OverridesSupport.Events.CanForceCompositingModeChanged);

[pfeldman, 2013/10/31 11:23:58]

You should only dispatch it if this.canForce != result.

[dgozman, 2013/10/31 12:39:50]

Done.

+                if (!result && WebInspector.settings.overrideDeviceMetrics.get())
+                    WebInspector.settings.overrideDeviceMetrics.set(false);
+            }
+        }
+        PageAgent.canForceCompositingMode(callback.bind(this));
+    },
+
+    __proto__: WebInspector.Object.prototype
 }