[DevTools] Allow overriding only the device scale factor.

Source/devtools/front_end/OverridesSupport.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 445 matching lines @@
     _deviceMetricsChanged: function()
     {
         if (this._deviceMetricsChangedListenerMuted)
             return;
         var metrics = WebInspector.OverridesSupport.DeviceMetrics.parseSetting(WebInspector.settings.overrideDeviceMetrics.get() ? WebInspector.settings.deviceMetrics.get() : "");
         if (!metrics.isValid())
             return;
 
         var dipWidth = Math.round(metrics.width / metrics.deviceScaleFactor);
         var dipHeight = Math.round(metrics.height / metrics.deviceScaleFactor);
+        var metricsOverrideEnabled = !!(dipWidth && dipHeight);
 
         // Disable override without checks.
-        if (dipWidth && dipHeight && WebInspector.OverridesSupport.isInspectingDevice()) {
+        if (metricsOverrideEnabled && WebInspector.OverridesSupport.isInspectingDevice()) {
             this._updateDeviceMetricsWarningMessage(WebInspector.UIString("Screen emulation on the device is not available."));
             return;
         }
 
-        PageAgent.setDeviceMetricsOverride(dipWidth, dipHeight, metrics.deviceScaleFactor, WebInspector.settings.emulateViewport.get(), WebInspector.settings.deviceFitWindow.get(), metrics.textAutosizing, metrics.fontScaleFactor(), apiCallback.bind(this));
+        PageAgent.setDeviceMetricsOverride(dipWidth, dipHeight, metricsOverrideEnabled ? metrics.deviceScaleFactor : 0, WebInspector.settings.emulateViewport.get(), WebInspector.settings.deviceFitWindow.get(), metrics.textAutosizing, metrics.fontScaleFactor(), apiCallback.bind(this));
         this.maybeHasActiveOverridesChanged();
 
         /**
          * @param {?Protocol.Error} error
          * @this {WebInspector.OverridesSupport}
          */
         function apiCallback(error)
         {
             if (error) {
                 this._updateDeviceMetricsWarningMessage(WebInspector.UIString("Screen emulation is not available on this page."));
                 return;
             }
 
-            var metricsOverrideEnabled = !!(dipWidth && dipHeight);
             var viewportEnabled =  WebInspector.settings.emulateViewport.get();
             this._updateDeviceMetricsWarningMessage(this._deviceMetricsOverrideEnabled !== metricsOverrideEnabled || (metricsOverrideEnabled && this._emulateViewportEnabled != viewportEnabled) ?
                 WebInspector.UIString("You might need to reload the page for proper user agent spoofing and viewport rendering.") : "");
             this._deviceMetricsOverrideEnabled = metricsOverrideEnabled;
             this._emulateViewportEnabled = viewportEnabled;
             this._deviceMetricsOverrideAppliedForTest();
         }
     },
 
     _deviceMetricsOverrideAppliedForTest: function()
@@ skipping 97 matching lines @@
     },
 
     __proto__: WebInspector.Object.prototype
 }
 
 
 /**
  * @type {!WebInspector.OverridesSupport}
  */
 WebInspector.overridesSupport;