Start incremental marking in idle time handler only if it is worthwhile.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 76046641cd4f07ee6b44262ae100e914bf03af61..762fcf348c035c6d56b3c4ca863d3c6dbcb50461 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -846,7 +846,7 @@ bool Heap::CollectGarbage(GarbageCollector collector, const char* gc_reason,
   // generator needs incremental marking to stay off after it aborted.
   if (!mark_compact_collector()->abort_incremental_marking() &&
       incremental_marking()->IsStopped() &&
-      incremental_marking()->WorthActivating() && NextGCIsLikelyToBeFull()) {
+      WorthActivatingIncrementalMarking()) {
     incremental_marking()->Start();
   }
 
@@ -4283,6 +4283,11 @@ void Heap::AdvanceIdleIncrementalMarking(intptr_t step_size) {
 }
 
 
+bool Heap::WorthActivatingIncrementalMarking() {
+  return incremental_marking()->WorthActivating() && NextGCIsLikelyToBeFull();
+}
+
+
 bool Heap::IdleNotification(int idle_time_in_ms) {
   // If incremental marking is off, we do not perform idle notification.
   if (!FLAG_incremental_marking) return true;
@@ -4298,7 +4303,8 @@ bool Heap::IdleNotification(int idle_time_in_ms) {
   bool result = false;
   switch (action.type) {
     case DO_INCREMENTAL_MARKING:
-      if (incremental_marking()->IsStopped()) {
+      if (incremental_marking()->IsStopped() &&
+          WorthActivatingIncrementalMarking()) {

[Hannes Payer (out of office), 2014/08/21 15:25:18]

As discussed offline, can we move that into GCIdleTimeHandler Compute?

         incremental_marking()->Start();
       }
       AdvanceIdleIncrementalMarking(action.parameter);