Introducing GlobalDictionary, a backing store for global objects.

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 00665e3ffdde2dcd3b0b6d16d2d3af4594aaf018..23afbc2566afe18902b8258bb657b24ca5030fc7 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -377,6 +377,7 @@ class MemoryChunk;
 class SeededNumberDictionary;
 class UnseededNumberDictionary;
 class NameDictionary;
+class GlobalDictionary;
 template <typename T> class MaybeHandle;
 template <typename T> class Handle;
 class Heap;