Mark faster when executing write barriers.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/159833002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19290 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/incremental-marking.h

@@ -100,7 +100,7 @@ class IncrementalMarking {
   // Do some marking every time this much memory has been allocated or that many
   // heavy (color-checking) write barriers have been invoked.
   static const intptr_t kAllocatedThreshold = 65536;
-  static const intptr_t kWriteBarriersInvokedThreshold = 65536;
+  static const intptr_t kWriteBarriersInvokedThreshold = 32768;
   // Start off by marking this many times more memory than has been allocated.
   static const intptr_t kInitialMarkingSpeed = 1;
   // But if we are promoting a lot of data we need to mark faster to keep up