Oilpan: Finsh incremental marking if RAILMode changes to LOADING

Change-Id: I63eae05326391dcb2c62f571ac13650a6e2967b0
Reviewed-on: https://chromium-review.googlesource.com/1148210Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578604}

third_party/blink/renderer/platform/heap/thread_state.h

@@ -572,6 +572,9 @@ class PLATFORM_EXPORT ThreadState final
   // Implementation for WebRAILModeObserver
   void OnRAILModeChanged(v8::RAILMode new_mode) override {
     should_optimize_for_load_time_ = new_mode == v8::RAILMode::PERFORMANCE_LOAD;
+    if (should_optimize_for_load_time_ && IsIncrementalMarking() &&
+        GetGCState() == GCState::kIncrementalMarkingStepScheduled)
+      ScheduleIncrementalMarkingFinalize();
   }
 
  private: