[blink] Support (semi-)transparent background colors in WebView/Frame.

third_party/WebKit/Source/web/DevToolsEmulator.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "web/DevToolsEmulator.h"
 
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/frame/VisualViewport.h"
@@ skipping 227 matching lines @@
       document->mediaQueryAffectingValueChanged();
   }
 }
 
 void DevToolsEmulator::disableDeviceEmulation() {
   if (!m_deviceMetricsEnabled)
     return;
 
   memoryCache()->evictResources();
   m_deviceMetricsEnabled = false;
-  m_webViewImpl->setBackgroundColorOverride(Color::transparent);
+  m_webViewImpl->clearBackgroundColorOverride();
   m_webViewImpl->page()->settings().setDeviceScaleAdjustment(
       m_embedderDeviceScaleAdjustment);
   disableMobileEmulation();
   m_webViewImpl->setCompositorDeviceScaleFactorOverride(0.f);
   m_webViewImpl->setPageScaleFactor(1.f);
   updateRootLayerTransform();
   // mainFrameImpl() could be null during cleanup or remote <-> local swap.
   if (m_webViewImpl->mainFrameImpl()) {
     if (Document* document =
             m_webViewImpl->mainFrameImpl()->frame()->document())
@@ skipping 272 matching lines @@
       m_lastPinchAnchorCss.reset();
       m_lastPinchAnchorDip.reset();
     }
     return true;
   }
 
   return false;
 }
 
 }  // namespace blink