[DevTools] Device mode: reset page scale when enabling and improve UI.

Source/devtools/front_end/sdk/OverridesSupport.js

Index: Source/devtools/front_end/sdk/OverridesSupport.js
diff --git a/Source/devtools/front_end/sdk/OverridesSupport.js b/Source/devtools/front_end/sdk/OverridesSupport.js
index 4557ca73e8d54025f1479905ad42a900d6006d7a..e10dff858a01eabd742115add99d69c45c4459a0 100644
--- a/Source/devtools/front_end/sdk/OverridesSupport.js
+++ b/Source/devtools/front_end/sdk/OverridesSupport.js
@@ -276,6 +276,8 @@ WebInspector.OverridesSupport.prototype = {
         if (this.canEmulate()) {
             this.settings._emulationEnabled.set(enabled);
             this.dispatchEventToListeners(WebInspector.OverridesSupport.Events.EmulationStateChanged);
+            if (enabled && this.settings.emulateResolution.get())
+                this._target.pageAgent().resetScrollAndPageScaleFactor();
         }
     },
 
@@ -332,7 +334,7 @@ WebInspector.OverridesSupport.prototype = {
         if (this._initialized) {
             this._deviceMetricsChanged();
             this._userAgentChanged();
-            PageAgent.resetScrollAndPageScaleFactor();
+            this._target.pageAgent().resetScrollAndPageScaleFactor();
         }
     },
 
@@ -464,6 +466,8 @@ WebInspector.OverridesSupport.prototype = {
             this._cssMediaChanged();
 
         this._deviceMetricsChanged();
+        if (this.settings.emulateResolution.get())
+            this._target.pageAgent().resetScrollAndPageScaleFactor();
 
         this._userAgentChanged();
 
@@ -572,7 +576,7 @@ WebInspector.OverridesSupport.prototype = {
          */
         function setDeviceMetricsOverride(finishCallback)
         {
-            PageAgent.setDeviceMetricsOverride(
+            this._target.pageAgent().setDeviceMetricsOverride(
                 overrideWidth, overrideHeight, this.settings.emulateResolution.get() ? this.settings.deviceScaleFactor.get() : 0,
                 this.settings.emulateMobile.get(), this._pageResizer ? false : this.settings.deviceFitWindow.get(), scale, 0, 0,
                 apiCallback.bind(this, finishCallback));
@@ -584,7 +588,7 @@ WebInspector.OverridesSupport.prototype = {
          */
         function clearDeviceMetricsOverride(finishCallback)
         {
-            PageAgent.clearDeviceMetricsOverride(apiCallback.bind(this, finishCallback));
+            this._target.pageAgent().clearDeviceMetricsOverride(apiCallback.bind(this, finishCallback));
         }
 
         /**