Make sure that there is enough time left before finishing incremental marking in idle notification.

src/gc-tracer.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_GC_TRACER_H_
 #define V8_GC_TRACER_H_
 
 namespace v8 {
 namespace internal {
 
@@ skipping 236 matching lines @@
   double MeanIncrementalMarkingDuration() const;
 
   // Compute the max step duration of the last incremental marking round.
   // Returns 0 if no incremental marking round has been completed.
   double MaxIncrementalMarkingDuration() const;
 
   // Compute the average incremental marking speed in bytes/second. Returns 0 if
   // no events have been recorded.
   intptr_t MarkingSpeedInBytesPerMillisecond() const;
 
+  // Returns the duration of the last incremental marking step.
+  double last_incremental_marking_step_duration() const {
+    return last_incremental_marking_step_duration_;
+  }
+
  private:
   // Print one detailed trace line in name=value format.
   // TODO(ernstm): Move to Heap.
   void PrintNVP() const;
 
   // Print one trace line.
   // TODO(ernstm): Move to Heap.
   void Print() const;
 
   // Compute the mean duration of the events in the given ring buffer.
@@ skipping 24 matching lines @@
   // Cumulative number of incremental marking steps since creation of tracer.
   int cumulative_incremental_marking_steps_;
 
   // Cumulative size of incremental marking steps (in bytes) since creation of
   // tracer.
   intptr_t cumulative_incremental_marking_bytes_;
 
   // Cumulative duration of incremental marking steps since creation of tracer.
   double cumulative_incremental_marking_duration_;
 
+  // Duration of last incremental marking step.
+  double last_incremental_marking_step_duration_;
+
   // Longest incremental marking step since start of marking.
   double longest_incremental_marking_step_;
 
   DISALLOW_COPY_AND_ASSIGN(GCTracer);
 };
 }
 }  // namespace v8::internal
 
 #endif  // V8_GC_TRACER_H_