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

src/heap/gc-idle-time-handler.h

Index: src/heap/gc-idle-time-handler.h
diff --git a/src/heap/gc-idle-time-handler.h b/src/heap/gc-idle-time-handler.h
index 76cdb9f21cd59d97fde49cc82382e73ffbd35427..5a842a85971f42823edc93cba4ca754c408f656a 100644
--- a/src/heap/gc-idle-time-handler.h
+++ b/src/heap/gc-idle-time-handler.h
@@ -49,6 +49,7 @@ class GCIdleTimeAction {
   intptr_t parameter;
 };
 
+
 class GCTracer;
 
 // The idle time handler makes decisions about which garbage collection
@@ -73,13 +74,18 @@ class GCIdleTimeHandler {
   // Maximum mark-compact time returned by EstimateMarkCompactTime.
   static const size_t kMaxMarkCompactTimeInMs;
 
+  struct HeapState {
+    int contexts_disposed;
+    size_t size_of_objects;
+    bool incremental_marking_stopped;
+    bool can_start_incremental_marking;
+  };
+
   GCIdleTimeHandler()
       : mark_compacts_since_idle_round_started_(0),
         scavenges_since_last_idle_round_(0) {}
 
-  GCIdleTimeAction Compute(int idle_time_in_ms, int contexts_disposed,
-                           size_t size_of_objects,
-                           bool incremental_marking_stopped,
+  GCIdleTimeAction Compute(int idle_time_in_ms, HeapState heap_state,
                            GCTracer* gc_tracer);
 
   void NotifyIdleMarkCompact() {