Add UMAs about Blink GC metrics

Source/platform/heap/Heap.h

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 928 matching lines @@
     // This is slow and should only be used for debug purposes.
     // It involves finding the heap page and scanning the heap page for an object header.
     static const GCInfo* findGCInfo(Address);
 #endif
 
     // Collect heap stats for all threads attached to the Blink
     // garbage collector. Should only be called during garbage
     // collection where threads are known to be at safe points.
     static void getStats(HeapStats*);
 
+    static uint64_t totalObjectSpaceInAllThreads();
+
     static bool isConsistentForGC();
     static void makeConsistentForGC();
 
     static void flushHeapDoesNotContainCache();
     static bool heapDoesNotContainCacheIsEmpty() { return s_heapDoesNotContainCache->isEmpty(); }
 
     // Return true if the last GC found a pointer into a heap page
     // during conservative scanning.
     static bool lastGCWasConservative() { return s_lastGCWasConservative; }
 
@@ skipping 1350 matching lines @@
 // to export. This forces it to export all the methods from ThreadHeap.
 template<> void ThreadHeap<FinalizedHeapObjectHeader>::addPageToHeap(const GCInfo*);
 template<> void ThreadHeap<HeapObjectHeader>::addPageToHeap(const GCInfo*);
 extern template class PLATFORM_EXPORT ThreadHeap<FinalizedHeapObjectHeader>;
 extern template class PLATFORM_EXPORT ThreadHeap<HeapObjectHeader>;
 #endif
 
 }
 
 #endif // Heap_h