Extending v8::GetHeapStatistics to return total available size.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 3a89095d0b7344512dbbd6658d816f09bd851322..7ad6f3bf58b546e8307323a2aab48007a214b41e 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -6869,6 +6869,7 @@ void Isolate::GetHeapStatistics(HeapStatistics* heap_statistics) {
   heap_statistics->total_heap_size_executable_ =
       heap->CommittedMemoryExecutable();
   heap_statistics->total_physical_size_ = heap->CommittedPhysicalMemory();
+  heap_statistics->total_available_size_ = heap->Available();
   heap_statistics->used_heap_size_ = heap->SizeOfObjects();
   heap_statistics->heap_size_limit_ = heap->MaxReserved();
 }