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

Source/core/inspector/InspectorPageAgent.cpp

 /*
  * Copyright (C) 2011 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 642 matching lines @@
     }
 
     if (fontScaleFactor <= 0) {
         *errorString = "fontScaleFactor must be positive";
         return;
     }
 
     if (!deviceMetricsChanged(width, height, deviceScaleFactor, fitWindow, fontScaleFactor, textAutosizing))
         return;
 
+    Settings& settings = m_page->settings();
+    if (width && height && !settings.acceleratedCompositingEnabled()) {
+        if (errorString)
+            *errorString = "Compositing mode is not supported";
+        return;
+    }
+
     m_state->setLong(PageAgentState::pageAgentScreenWidthOverride, width);
     m_state->setLong(PageAgentState::pageAgentScreenHeightOverride, height);
     m_state->setDouble(PageAgentState::pageAgentDeviceScaleFactorOverride, deviceScaleFactor);
     m_state->setBoolean(PageAgentState::pageAgentFitWindow, fitWindow);
     m_state->setDouble(PageAgentState::textAutosizingFontScaleFactorOverride, fontScaleFactor);
     m_state->setBoolean(PageAgentState::pageAgentTextAutosizingOverride, textAutosizing);
 
     updateViewMetrics(width, height, deviceScaleFactor, fitWindow);
 }
 
@@ skipping 507 matching lines @@
     }
 }
 
 void InspectorPageAgent::applyEmulatedMedia(String* media)
 {
     String emulatedMedia = m_state->getString(PageAgentState::pageAgentEmulatedMedia);
     if (!emulatedMedia.isEmpty())
         *media = emulatedMedia;
 }
 
+void InspectorPageAgent::canForceCompositingMode(ErrorString* errorString, bool* result)
+{
+    *result = m_page->settings().acceleratedCompositingEnabled();
+}
+
 void InspectorPageAgent::setForceCompositingMode(ErrorString* errorString, bool force)
 {
     Settings& settings = m_page->settings();
     if (force && !settings.acceleratedCompositingEnabled()) {
         if (errorString)
             *errorString = "Compositing mode is not supported";
         return;
     }
     m_state->setBoolean(PageAgentState::forceCompositingMode, force);
     if (settings.forceCompositingMode() == force)
@@ skipping 32 matching lines @@
 }
 
 void InspectorPageAgent::setShowViewportSizeOnResize(ErrorString*, bool show, const bool* showGrid)
 {
     m_state->setBoolean(PageAgentState::showSizeOnResize, show);
     m_state->setBoolean(PageAgentState::showGridOnResize, showGrid && *showGrid);
 }
 
 } // namespace WebCore