Reset context disposed counter after executing the idle garbage collection operation.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/552723004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23948 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap/heap.cc

@@ -4316,7 +4316,6 @@ bool Heap::IdleNotification(int idle_time_in_ms) {
   GCIdleTimeAction action =
       gc_idle_time_handler_.Compute(idle_time_in_ms, heap_state);
 
-  contexts_disposed_ = 0;
   bool result = false;
   switch (action.type) {
     case DO_INCREMENTAL_MARKING:
@@ -4352,6 +4351,7 @@ bool Heap::IdleNotification(int idle_time_in_ms) {
     PrintF("]\n");
   }
 
+  contexts_disposed_ = 0;
   return result;
 }