Introduce ThreadState::isOnThreadHeap() helper predicate.

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

Index: third_party/WebKit/Source/platform/heap/ThreadState.h
diff --git a/third_party/WebKit/Source/platform/heap/ThreadState.h b/third_party/WebKit/Source/platform/heap/ThreadState.h
index a8c771b8db65a1b8b443db26b52c31adad5d5228..284a3de876ca52e6c0b12235a3698d34e5d7d520 100644
--- a/third_party/WebKit/Source/platform/heap/ThreadState.h
+++ b/third_party/WebKit/Source/platform/heap/ThreadState.h
@@ -573,6 +573,15 @@ class PLATFORM_EXPORT ThreadState {
 
   static const char* gcReasonString(BlinkGC::GCReason);
 
+  // Returns |true| if |object| resides on this thread's heap.
+  // It is well-defined to call this method on any heap allocated
+  // reference, provided its associated heap hasn't been detached
+  // and shut down. Its behavior is undefined for any other pointer
+  // value.
+  bool isOnThreadHeap(const void* object) const {
+    return &fromObject(object)->heap() == &heap();
+  }
+
  private:
   template <typename T>
   friend class PrefinalizerRegistration;