Dramatically speed up detailed heap snapshot generation.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 3d88568882350628c8f4895c41c0265c9f502f8f..06657017a8af1ffa7cfbe4e3853b547fdc3ab7ff 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1587,6 +1587,7 @@ class JSObject: public HeapObject {
   inline int GetHeaderSize();
 
   inline int GetInternalFieldCount();
+  inline int GetInternalFieldOffset(int index);
   inline Object* GetInternalField(int index);
   inline void SetInternalField(int index, Object* value);
 
@@ -1704,6 +1705,7 @@ class JSObject: public HeapObject {
   inline Object* FastPropertyAtPut(int index, Object* value);
 
   // Access to in object properties.
+  inline int GetInObjectPropertyOffset(int index);
   inline Object* InObjectPropertyAt(int index);
   inline Object* InObjectPropertyAtPut(int index,
                                        Object* value,