Make sure we do not start incremental marking in idle notification when...

Make sure we do not start incremental marking in idle notification when incremental marking is turned off via flags.

BUG=chromium:498315
LOG=n

Review URL: https://codereview.chromium.org/1177953002

Cr-Commit-Position: refs/heads/master@{#28925}

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "src/flags.h"
 #include "src/heap/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/utils.h"
@@ -322,8 +323,9 @@ GCIdleTimeAction GCIdleTimeHandler::Action(double idle_time_in_ms,
     }
   }
 
-  if (heap_state.incremental_marking_stopped &&
-      !heap_state.can_start_incremental_marking && !reduce_memory) {
+  if (!FLAG_incremental_marking ||
+      (heap_state.incremental_marking_stopped &&
+       !heap_state.can_start_incremental_marking && !reduce_memory)) {
     return NothingOrDone();
   }