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

src/gc-tracer.cc

Index: src/gc-tracer.cc
diff --git a/src/gc-tracer.cc b/src/gc-tracer.cc
index 74a2aa873f1cb635ad6a2401c01cc4640db7f1c0..58a524593ea907a98307fed37edda33b103a7aad 100644
--- a/src/gc-tracer.cc
+++ b/src/gc-tracer.cc
@@ -75,6 +75,7 @@ GCTracer::GCTracer(Heap* heap)
       cumulative_incremental_marking_steps_(0),
       cumulative_incremental_marking_bytes_(0),
       cumulative_incremental_marking_duration_(0.0),
+      last_incremental_marking_step_duration_(0.0),
       longest_incremental_marking_step_(0.0) {
   current_ = Event(Event::START, NULL, NULL);
   current_.end_time = base::OS::TimeCurrentMillis();
@@ -172,6 +173,7 @@ void GCTracer::AddIncrementalMarkingStep(double duration, intptr_t bytes) {
   cumulative_incremental_marking_steps_++;
   cumulative_incremental_marking_bytes_ += bytes;
   cumulative_incremental_marking_duration_ += duration;
+  last_incremental_marking_step_duration_ = duration;
   longest_incremental_marking_step_ =
       Max(longest_incremental_marking_step_, duration);
 }