Implement frame attribution (FrameBlamer)

third_party/WebKit/public/platform/Platform.h

Index: third_party/WebKit/public/platform/Platform.h
diff --git a/third_party/WebKit/public/platform/Platform.h b/third_party/WebKit/public/platform/Platform.h
index aa24d26c0328c6ad64203e7f699742a017c0243f..77a92599716e998d647981dfc10d0c20bf87ac87 100644
--- a/third_party/WebKit/public/platform/Platform.h
+++ b/third_party/WebKit/public/platform/Platform.h
@@ -35,6 +35,7 @@
 #include <windows.h>
 #endif
 
+#include "BlameContext.h"
 #include "UserMetricsAction.h"
 #include "WebAudioDevice.h"
 #include "WebCommon.h"
@@ -358,6 +359,10 @@ public:
     // embedder.
     virtual WebThread* currentThread() { return nullptr; }
 
+    // Returns a blame context for attributing top-level work which does not
+    // belong to a particular frame scope.
+    virtual BlameContext* topLevelBlameContext() { return nullptr; }
+
     // Resources -----------------------------------------------------------
 
     // Returns a blob of data corresponding to the named resource.