Introduce infrastructure for tracing ScriptWrappables.

third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h

Index: third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h b/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h
index aab62ffe582846471e05607dd8a09c861cb5d8c3..d5804194b83f5cf8f4401829bd718b70c97d6264 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h
+++ b/third_party/WebKit/Source/bindings/core/v8/ActiveScriptWrappable.h
@@ -11,6 +11,7 @@
 namespace blink {
 
 class ScriptWrappable;
+class ScriptWrappableVisitor;
 
 /**
  * Classes deriving from ActiveScriptWrappable will be registered in a
@@ -22,6 +23,8 @@ class CORE_EXPORT ActiveScriptWrappable {
 public:
     explicit ActiveScriptWrappable(ScriptWrappable*);
 
+    static void traceActiveScriptWrappables(ScriptWrappableVisitor*);
+
     virtual bool hasPendingActivity() const = 0;
 
     ScriptWrappable* toScriptWrappable() const;