Expose a lower bound of malloc'd memory via heap statistics

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 38c22db645ffd95e312788502e23887b5a3e3d7a..9f5e7be094780a411f7849af1d2a99663de27cd0 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -5490,13 +5490,15 @@ bool v8::V8::Dispose() {
   return true;
 }
 
-
-HeapStatistics::HeapStatistics(): total_heap_size_(0),
-                                  total_heap_size_executable_(0),
-                                  total_physical_size_(0),
-                                  used_heap_size_(0),
-                                  heap_size_limit_(0) { }
-
+HeapStatistics::HeapStatistics()
+    : total_heap_size_(0),
+      total_heap_size_executable_(0),
+      total_physical_size_(0),
+      total_available_size_(0),
+      used_heap_size_(0),
+      heap_size_limit_(0),
+      malloced_memory_(0),
+      does_zap_garbage_(0) {}
 
 HeapSpaceStatistics::HeapSpaceStatistics(): space_name_(0),
                                             space_size_(0),
@@ -7393,6 +7395,8 @@ void Isolate::GetHeapStatistics(HeapStatistics* heap_statistics) {
   heap_statistics->total_available_size_ = heap->Available();
   heap_statistics->used_heap_size_ = heap->SizeOfObjects();
   heap_statistics->heap_size_limit_ = heap->MaxReserved();
+  heap_statistics->malloced_memory_ =
+      isolate->allocator()->GetCurrentMemoryUsage();
   heap_statistics->does_zap_garbage_ = heap->ShouldZapGarbage();
 }