SameThreadCheckedMember<>: verify same-thread usage of heap references.

third_party/WebKit/Source/platform/heap/Visitor.h

Index: third_party/WebKit/Source/platform/heap/Visitor.h
diff --git a/third_party/WebKit/Source/platform/heap/Visitor.h b/third_party/WebKit/Source/platform/heap/Visitor.h
index 6b8c13a66fe25a8ab9fd628c1d42c03703e5396e..82ea4331ab7f4c3946c215147d5271045bae09d4 100644
--- a/third_party/WebKit/Source/platform/heap/Visitor.h
+++ b/third_party/WebKit/Source/platform/heap/Visitor.h
@@ -51,6 +51,8 @@ class TraceTrait;
 class ThreadState;
 class Visitor;
 template <typename T>
+class SameThreadCheckedMember;
+template <typename T>
 class TraceWrapperMember;
 
 // The TraceMethodDelegate is used to convert a trace method for type T to a
@@ -163,6 +165,11 @@ class VisitorHelper {
     trace(*(static_cast<const Member<T>*>(&t)));
   }
 
+  template <typename T>
+  void trace(const SameThreadCheckedMember<T>& t) {
+    trace(*(static_cast<const Member<T>*>(&t)));
+  }
+
   // Fallback method used only when we need to trace raw pointers of T.
   // This is the case when a member is a union where we do not support members.
   template <typename T>