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

BUG=chromium:727569

Review-Url: https://codereview.chromium.org/2910203002
Cr-Commit-Position: refs/heads/master@{#45599}

include/v8.h

@@ -7147,6 +7147,17 @@ class V8_EXPORT Isolate {
    */
   void RemoveGCEpilogueCallback(GCCallback callback);
 
+  typedef size_t (*GetExternallyAllocatedMemoryInBytesCallback)();
+
+  /**
+   * Set the callback that tells V8 how much memory is currently allocated
+   * externally of the V8 heap. Ideally this memory is somehow connected to V8
+   * objects and may get freed-up when the corresponding V8 objects get
+   * collected by a V8 garbage collection.
+   */
+  void SetGetExternallyAllocatedMemoryInBytesCallback(
+      GetExternallyAllocatedMemoryInBytesCallback callback);
+
   /**
    * Forcefully terminate the current thread of JavaScript execution
    * in the given isolate.

src/api.cc

@@ -8260,6 +8260,12 @@ void Isolate::SetEmbedderHeapTracer(EmbedderHeapTracer* tracer) {
   isolate->heap()->SetEmbedderHeapTracer(tracer);
 }
 
+void Isolate::SetGetExternallyAllocatedMemoryInBytesCallback(
+    GetExternallyAllocatedMemoryInBytesCallback callback) {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  isolate->heap()->SetGetExternallyAllocatedMemoryInBytesCallback(callback);
+}
+
 void Isolate::TerminateExecution() {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   isolate->stack_guard()->RequestTerminateExecution();

src/heap/heap.cc

@@ -381,6 +381,8 @@ void Heap::PrintShortHeapStatistics() {
                this->CommittedMemory() / KB);
   PrintIsolate(isolate_, "External memory reported: %6" PRId64 " KB\n",
                external_memory_ / KB);
+  PrintIsolate(isolate_, "External memory global %zu KB\n",
+               external_memory_callback_() / KB);
   PrintIsolate(isolate_, "Total time spent in GC  : %.1f ms\n",
                total_gc_time_ms_);
 }
@@ -964,7 +966,6 @@ void Heap::ReportExternalMemoryPressure() {
   }
 }
 
-
 void Heap::EnsureFillerObjectAtTop() {
   // There may be an allocation memento behind objects in new space. Upon
   // evacuation of a non-full new space (or if we are on the last page) there
@@ -5743,6 +5744,9 @@ bool Heap::SetUp() {
       *this, ScavengeJob::kBytesAllocatedBeforeNextIdleTask);
   new_space()->AddAllocationObserver(idle_scavenge_observer_);
 
+  SetGetExternallyAllocatedMemoryInBytesCallback(
+      DefaultGetExternallyAllocatedMemoryInBytesCallback);
+
   return true;
 }
 

src/heap/heap.h

@@ -1175,6 +1175,14 @@ class Heap {
   // 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();
 
@@ -1664,6 +1672,10 @@ class Heap {
     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)
@@ -2282,6 +2294,8 @@ class Heap {
   List<GCCallbackPair> gc_epilogue_callbacks_;
   List<GCCallbackPair> gc_prologue_callbacks_;
 
+  GetExternallyAllocatedMemoryInBytesCallback external_memory_callback_;
+
   int deferred_counters_[v8::Isolate::kUseCounterFeatureCount];
 
   GCTracer* tracer_;