[api] Add an API function to set the GetExternallyAllocatedMemoryInBytesCallback.

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <vector>
 
@@ skipping 1157 matching lines @@
       int flags, GarbageCollectionReason gc_reason,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
   // Last hope GC, should try to squeeze as much as possible.
   void CollectAllAvailableGarbage(GarbageCollectionReason gc_reason);
 
   // Reports and external memory pressure event, either performs a major GC or
   // completes incremental marking in order to free external resources.
   void ReportExternalMemoryPressure();
 
+  typedef v8::Isolate::GetExternallyAllocatedMemoryInBytesCallback
+      GetExternallyAllocatedMemoryInBytesCallback;
+
+  void SetGetExternallyAllocatedMemoryInBytesCallback(
+      GetExternallyAllocatedMemoryInBytesCallback callback) {
+    external_memory_callback_ = callback;
+  }
+
   // Invoked when GC was requested via the stack guard.
   void HandleGCRequest();
 
   // ===========================================================================
   // Iterators. ================================================================
   // ===========================================================================
 
   // Iterates over all roots in the heap.
   void IterateRoots(RootVisitor* v, VisitMode mode);
   // Iterates over all strong roots in the heap.
@@ skipping 469 matching lines @@
   Heap();
 
   static String* UpdateNewSpaceReferenceInExternalStringTableEntry(
       Heap* heap, Object** pointer);
 
   // Selects the proper allocation space based on the pretenuring decision.
   static AllocationSpace SelectSpace(PretenureFlag pretenure) {
     return (pretenure == TENURED) ? OLD_SPACE : NEW_SPACE;
   }
 
+  static size_t DefaultGetExternallyAllocatedMemoryInBytesCallback() {
+    return 0;
+  }
+
 #define ROOT_ACCESSOR(type, name, camel_name) \
   inline void set_##name(type* value);
   ROOT_LIST(ROOT_ACCESSOR)
 #undef ROOT_ACCESSOR
 
   StoreBuffer* store_buffer() { return store_buffer_; }
 
   void set_current_gc_flags(int flags) {
     current_gc_flags_ = flags;
     DCHECK(!ShouldFinalizeIncrementalMarking() ||
@@ skipping 598 matching lines @@
   // contains Smi(0) while marking is not active.
   Object* encountered_weak_collections_;
 
   Object* encountered_weak_cells_;
 
   Object* encountered_transition_arrays_;
 
   List<GCCallbackPair> gc_epilogue_callbacks_;
   List<GCCallbackPair> gc_prologue_callbacks_;
 
+  GetExternallyAllocatedMemoryInBytesCallback external_memory_callback_;
+
   int deferred_counters_[v8::Isolate::kUseCounterFeatureCount];
 
   GCTracer* tracer_;
 
   size_t promoted_objects_size_;
   double promotion_ratio_;
   double promotion_rate_;
   size_t semi_space_copied_object_size_;
   size_t previous_semi_space_copied_object_size_;
   double semi_space_copied_rate_;
@@ skipping 365 matching lines @@
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 V8_EXPORT_PRIVATE const char* AllocationSpaceName(AllocationSpace space);
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_