Addding support for -webkit-background-blend-mode to blink.

Tools/DumpRenderTree/chromium/TestRunner/src/TestRunner.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2010 Pawel Hajdan (phajdan.jr@chromium.org)
  * Copyright (C) 2012 Apple 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
@@ skipping 1615 matching lines @@
     else if (key == "WebKitEnableCaretBrowsing")
         prefs->caretBrowsingEnabled = cppVariantToBool(value);
     else if (key == "WebKitAllowDisplayingInsecureContent")
         prefs->allowDisplayOfInsecureContent = cppVariantToBool(value);
     else if (key == "WebKitAllowRunningInsecureContent")
         prefs->allowRunningOfInsecureContent = cppVariantToBool(value);
     else if (key == "WebKitCSSCustomFilterEnabled")
         prefs->cssCustomFilterEnabled = cppVariantToBool(value);
     else if (key == "WebKitShouldRespectImageOrientation")
         prefs->shouldRespectImageOrientation = cppVariantToBool(value);
+    else if (key == "WebKitAcceleratedCompositingEnabled")

[Stephen White, 2013/05/17 19:16:23]

I don't think there's any need to plumb this through. In Chromium, we usually
use -webkit-transform: translateZ(0); to turn on acceleration, and simply omit
that style to leave it off. 

+        prefs->acceleratedCompositingEnabled = cppVariantToBool(value);
     else if (key == "WebKitWebAudioEnabled")
         WEBKIT_ASSERT(cppVariantToBool(value));
     else {
         string message("Invalid name for preference: ");
         message.append(key);
         printErrorMessage(message);
     }
     m_delegate->applyPreferences();
 }
 
@@ skipping 390 matching lines @@
     result->setNull();
 }
 
 void TestRunner::setPointerLockWillFailSynchronously(const CppArgumentList&, CppVariant* result)
 {
     m_pointerLockPlannedResult = PointerLockWillFailSync;
     result->setNull();
 }
 
 }