Fix compile error after r19955

BUG=None
TBR=svenpanne@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/201573002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19956 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8-profiler.h

@@ -36,7 +36,7 @@
 namespace v8 {
 
 class HeapGraphNode;
-class HeapStatsUpdate;
+struct HeapStatsUpdate;
 
 typedef uint32_t SnapshotObjectId;