Distinguish weak references in heap snapshots, group GC roots.

src/profile-generator-inl.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 77 matching lines @@
     // To avoid confusing people, let's put all these entries into
     // one bucket.
     case OTHER:
     case EXTERNAL:
       return program_entry_;
     default: return NULL;
   }
 }
 
 
+uint64_t HeapObjectsMap::GetNthGcSubrootId(int delta) {
+  return kGcRootsObjectId + delta * kObjectIdStep;
+}
+
+
+HeapObject* V8HeapExplorer::GetNthGcSubrootObject(int delta) {
+  return reinterpret_cast<HeapObject*>(
+      reinterpret_cast<char*>(kFirstGcSubrootObject) +
+      delta * HeapObjectsMap::kObjectIdStep);
+}
+
+
+int V8HeapExplorer::GetGcSubrootOrder(HeapObject* subroot) {
+  return (reinterpret_cast<char*>(subroot) -
+          reinterpret_cast<char*>(kFirstGcSubrootObject)) /
+      HeapObjectsMap::kObjectIdStep;
+}
+
+
 uint64_t HeapEntry::id() {
   union {
     Id stored_id;
     uint64_t returned_id;
   } id_adaptor = {id_};
   return id_adaptor.returned_id;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROFILE_GENERATOR_INL_H_