Perform smaller marking steps incrementally in idle notification.

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

 // 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.
 
 #include "src/heap/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/utils.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 232 matching lines @@
   if (heap_state.sweeping_in_progress &&
       static_cast<size_t>(idle_time_in_ms) >= kMinTimeForFinalizeSweeping) {
     return GCIdleTimeAction::FinalizeSweeping();
   }
 
   if (heap_state.incremental_marking_stopped &&
       !heap_state.can_start_incremental_marking) {
     return GCIdleTimeAction::Nothing();
   }
   size_t step_size = EstimateMarkingStepSize(
-      static_cast<size_t>(idle_time_in_ms),
+      static_cast<size_t>(kIncrementalMarkingStepTimeInMs),
       heap_state.incremental_marking_speed_in_bytes_per_ms);
   return GCIdleTimeAction::IncrementalMarking(step_size);
 }
 }
 }