Simple BlinkGC heap compaction.

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

Index: third_party/WebKit/Source/platform/heap/BlinkGC.h
diff --git a/third_party/WebKit/Source/platform/heap/BlinkGC.h b/third_party/WebKit/Source/platform/heap/BlinkGC.h
index a0c271d948ea3a4dd4349e1162666ebe84e608e2..14200a44c1d49d3cd20da0fa30f9983fb1bac92c 100644
--- a/third_party/WebKit/Source/platform/heap/BlinkGC.h
+++ b/third_party/WebKit/Source/platform/heap/BlinkGC.h
@@ -25,6 +25,22 @@ using WeakCallback = VisitorCallback;
 using EphemeronCallback = VisitorCallback;
 using PreFinalizerCallback = bool (*)(void*);
 
+// Simple alias to avoid heap compaction type signatures turning into
+// a sea of generic |void*|s.
+using MovableReference = void*;
+
+// Heap compaction supports registering callbacks that are to be invoked
+// when an object is moved during compaction. This is to support internal
+// location fixups that need to happen as a result.
+//
+// i.e., when the object residing at |from| is moved to |to| by the compaction
+// pass, invoke the callback to adjust any internal references that now need
+// to be |to|-relative.
+using MovingObjectCallback = void (*)(void* callbackData,
+                                      MovableReference from,
+                                      MovableReference to,
+                                      size_t);
+
 // List of typed arenas. The list is used to generate the implementation
 // of typed arena related methods.
 //