Detailed heap snapshot usability improvement.

src/profile-generator.h

Index: src/profile-generator.h
diff --git a/src/profile-generator.h b/src/profile-generator.h
index aefe1a0f607df3ceb75321ee5daf745c13f789d9..cbd9373d2abb521b8fd7a7ec7da2314e0a704d40 100644
--- a/src/profile-generator.h
+++ b/src/profile-generator.h
@@ -1026,6 +1026,7 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   DISALLOW_COPY_AND_ASSIGN(V8HeapExplorer);
 };
 
+class NativeGroupRetainedObjectInfo;
 
 // An implementation of retained native objects extractor.
 class NativeObjectsExplorer : public HeapEntriesAllocator {
@@ -1057,6 +1058,12 @@ class NativeObjectsExplorer : public HeapEntriesAllocator {
         (reinterpret_cast<v8::RetainedObjectInfo*>(key1))->IsEquivalent(
             reinterpret_cast<v8::RetainedObjectInfo*>(key2));
   }
+  INLINE(static bool StringsMatch(void* key1, void* key2)) {
+    return strcmp(reinterpret_cast<char*>(key1),
+                  reinterpret_cast<char*>(key2)) == 0;
+  }
+
+  NativeGroupRetainedObjectInfo* FindOrAddGroupInfo(const char* label);
 
   HeapSnapshot* snapshot_;
   HeapSnapshotsCollection* collection_;
@@ -1065,6 +1072,7 @@ class NativeObjectsExplorer : public HeapEntriesAllocator {
   HeapObjectsSet in_groups_;
   // RetainedObjectInfo* -> List<HeapObject*>*
   HashMap objects_by_info_;
+  HashMap native_groups_;
   // Used during references extraction.
   SnapshotFillerInterface* filler_;