New Heap profiler: fix JSON serialization of aggregated profiles.

test/cctest/test-heap-profiler.cc

Index: test/cctest/test-heap-profiler.cc
diff --git a/test/cctest/test-heap-profiler.cc b/test/cctest/test-heap-profiler.cc
index 4dd7fe823f26d77807e19aecc4c22fdd89b15205..95314d74a4157c40904447df60eab5b18bc9834b 100644
--- a/test/cctest/test-heap-profiler.cc
+++ b/test/cctest/test-heap-profiler.cc
@@ -1178,4 +1178,19 @@ TEST(HeapSnapshotJSONSerializationAborting) {
   CHECK_EQ(0, stream.eos_signaled());
 }
 
+
+// Must not crash in debug mode.
+TEST(AggregatedHeapSnapshotJSONSerialization) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  const v8::HeapSnapshot* snapshot =
+      v8::HeapProfiler::TakeSnapshot(
+          v8::String::New("agg"), v8::HeapSnapshot::kAggregated);
+  TestJSONStream stream;
+  snapshot->Serialize(&stream, v8::HeapSnapshot::kJSON);
+  CHECK_GT(stream.size(), 0);
+  CHECK_EQ(1, stream.eos_signaled());
+}
+
 #endif  // ENABLE_LOGGING_AND_PROFILING