Adding WebThread and new BlinkPlatformImpl for utility thread.

content/utility/utility_thread_impl.h

Index: content/utility/utility_thread_impl.h
diff --git a/content/utility/utility_thread_impl.h b/content/utility/utility_thread_impl.h
index 4f0fa3f18916e7a7cc3f942661b4097e0ee24389..3b1d66d65d4407269c4de80f3a6b0559e74199a9 100644
--- a/content/utility/utility_thread_impl.h
+++ b/content/utility/utility_thread_impl.h
@@ -20,6 +20,7 @@ class FilePath;
 
 namespace content {
 class BlinkPlatformImpl;
+class UtilityBlinkPlatformImpl;
 
 #if defined(COMPILER_MSVC)
 // See explanation for other RenderViewHostImpl which is the same issue.
@@ -56,7 +57,7 @@ class UtilityThreadImpl : public UtilityThread,
   // True when we're running in batch mode.
   bool batch_mode_;
 
-  scoped_ptr<BlinkPlatformImpl> blink_platform_impl_;
+  scoped_ptr<UtilityBlinkPlatformImpl> blink_platform_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(UtilityThreadImpl);
 };