Provide more accurate results about used heap size via GetHeapStatistics.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index 94d05555ec556276834a381ad68786266f433e77..fbe66ecd74627eade4ea57fe233b3f50ff21e33d 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -1095,3 +1095,32 @@ TEST(TestInternalWeakListsTraverseWithGC) {
     ctx[i]->Exit();
   }
 }
+
+
+TEST(TestSizeOfObjectsVsHeapIteratorPrecision) {
+  InitializeVM();
+  intptr_t size_of_objects_1 = Heap::SizeOfObjects();
+  HeapIterator iterator(HeapIterator::kPreciseFiltering);
+  intptr_t size_of_objects_2 = 0;
+  for (HeapObject* obj = iterator.next();
+       obj != NULL;
+       obj = iterator.next()) {
+    size_of_objects_2 += obj->Size();
+  }
+  // Delta must be within 1% of the larger result.
+  if (size_of_objects_1 > size_of_objects_2) {
+    intptr_t delta = size_of_objects_1 - size_of_objects_2;
+    PrintF("Heap::SizeOfObjects: %" V8_PTR_PREFIX "d, "
+           "Iterator: %" V8_PTR_PREFIX "d, "
+           "delta: %" V8_PTR_PREFIX "d\n",
+           size_of_objects_1, size_of_objects_2, delta);
+    CHECK_GT(size_of_objects_1 / 100, delta);
+  } else {
+    intptr_t delta = size_of_objects_2 - size_of_objects_1;
+    PrintF("Heap::SizeOfObjects: %" V8_PTR_PREFIX "d, "
+           "Iterator: %" V8_PTR_PREFIX "d, "
+           "delta: %" V8_PTR_PREFIX "d\n",
+           size_of_objects_1, size_of_objects_2, delta);
+    CHECK_GT(size_of_objects_2 / 100, delta);
+  }
+}