Make Isolate::GetHeapStatistics robust against half-initialized isolates.

The (deprecated) non-Isolate GetHeapStatistics contains the same check.

BUG=2591

Review URL: https://codereview.chromium.org/12965013
Patch from Marja Hölttä <marja@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14079 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/api.cc

@@ -5971,6 +5971,14 @@ void Isolate::Exit() {
 
 void Isolate::GetHeapStatistics(HeapStatistics* heap_statistics) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  if (!isolate->IsInitialized()) {
+    heap_statistics->total_heap_size_ = 0;
+    heap_statistics->total_heap_size_executable_ = 0;
+    heap_statistics->total_physical_size_ = 0;
+    heap_statistics->used_heap_size_ = 0;
+    heap_statistics->heap_size_limit_ = 0;
+    return;
+  }
   i::Heap* heap = isolate->heap();
   heap_statistics->total_heap_size_ = heap->CommittedMemory();
   heap_statistics->total_heap_size_executable_ =