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

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

Index: Tools/DumpRenderTree/chromium/TestRunner/src/TestRunner.cpp
diff --git a/Tools/DumpRenderTree/chromium/TestRunner/src/TestRunner.cpp b/Tools/DumpRenderTree/chromium/TestRunner/src/TestRunner.cpp
index 9d38dd97c34aee109d39364179ac275f622011ab..dd04d41c2fc03b22afd2b230f86dfc964401635f 100644
--- a/Tools/DumpRenderTree/chromium/TestRunner/src/TestRunner.cpp
+++ b/Tools/DumpRenderTree/chromium/TestRunner/src/TestRunner.cpp
@@ -1633,6 +1633,8 @@ void TestRunner::overridePreference(const CppArgumentList& arguments, CppVariant
         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 {