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

Source/devtools/front_end/OverridesView.js

Index: Source/devtools/front_end/OverridesView.js
diff --git a/Source/devtools/front_end/OverridesView.js b/Source/devtools/front_end/OverridesView.js
index 6fd8e757a6b741b6ead61294742082604c318e02..649b32f66fbc1ee58186b93f69ab45b3dc30d6bd 100644
--- a/Source/devtools/front_end/OverridesView.js
+++ b/Source/devtools/front_end/OverridesView.js
@@ -368,7 +368,7 @@ WebInspector.OverridesView.DeviceTab._tablets = [
      "1280x800x1x0x1"],
     ["Samsung Galaxy Tab",
      "Mozilla/5.0 (Linux; U; Android 2.2; en-us; SCH-I800 Build/FROYO) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1",
-     "1024x600x0x1"],
+     "1024x600x1x0x1"],
 ];
 
 WebInspector.OverridesView.DeviceTab.prototype = {
@@ -426,6 +426,7 @@ WebInspector.OverridesView.ViewportTab = function()
     const metricsSetting = WebInspector.settings.deviceMetrics.get();
     var metrics = WebInspector.OverridesSupport.DeviceMetrics.parseSetting(metricsSetting);
     var checkbox = this._createSettingCheckbox(WebInspector.UIString("Emulate viewport"), WebInspector.settings.overrideDeviceMetrics, this._onMetricsCheckboxClicked.bind(this));
+    this._overrideDeviceMetricsCheckbox = checkbox.querySelector("input");
     WebInspector.settings.deviceMetrics.addChangeListener(this._updateDeviceMetricsElement, this);
 
     this.element.appendChild(checkbox);
@@ -433,6 +434,8 @@ WebInspector.OverridesView.ViewportTab = function()
     this.element.appendChild(this._createMediaEmulationElement());
     this._onMetricsCheckboxClicked(WebInspector.settings.overrideDeviceMetrics.get());
 
+    WebInspector.overridesSupport.addEventListener(WebInspector.OverridesSupport.Events.CanForceCompositingModeChanged, this._canForceCompositingModeChanged, this);
+    this._canForceCompositingModeChanged();
 }
 
 WebInspector.OverridesView.ViewportTab.prototype = {
@@ -494,6 +497,7 @@ WebInspector.OverridesView.ViewportTab.prototype = {
     _createDeviceMetricsElement: function(metrics)
     {
         var fieldsetElement = WebInspector.SettingsTab.createSettingFieldset(WebInspector.settings.overrideDeviceMetrics);
+        this._overrideDeviceMetricsFieldset = fieldsetElement;
         fieldsetElement.id = "metrics-override-section";
 
         function swapDimensionsClicked(event)
@@ -557,6 +561,12 @@ WebInspector.OverridesView.ViewportTab.prototype = {
             this._textAutosizingOverrideCheckbox.checked = metrics.textAutosizing;
     },
 
+    _canForceCompositingModeChanged: function()
+    {
+        this._overrideDeviceMetricsFieldset.disabled = !WebInspector.overridesSupport.canForceCompositingMode;
+        this._overrideDeviceMetricsCheckbox.disabled = !WebInspector.overridesSupport.canForceCompositingMode;
+    },
+
     _createMediaEmulationElement: function()
     {
         var checkbox = WebInspector.SettingsTab.createSettingCheckbox(WebInspector.UIString("CSS media"), WebInspector.settings.overrideCSSMedia, true);