heap: Restart concurrent markers when v8 helps

If the v8 marker is fast it can help Oilpan with marking.
This is a good opportunity to restart any concurrent markers that died.

Bug: 986235
Change-Id: I47cbde413e875206d0cd468699f6309d06222f6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2002614
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733613}

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

@@ -1217,7 +1217,7 @@ void ThreadState::IncrementalMarkingStep(BlinkGC::StackState stack_state,
 
   if (base::FeatureList::IsEnabled(
           blink::features::kBlinkHeapConcurrentMarking)) {
-    complete = complete && ConcurrentMarkingStep();
+    complete = ConcurrentMarkingStep() && complete;
   }
 
   if (complete) {

third_party/blink/renderer/platform/heap/unified_heap_controller.cc

@@ -134,6 +134,11 @@ bool UnifiedHeapController::AdvanceTracing(double deadline_in_ms) {
     base::TimeTicks deadline =
         base::TimeTicks() + base::TimeDelta::FromMillisecondsD(deadline_in_ms);
     is_tracing_done_ = thread_state_->MarkPhaseAdvanceMarking(deadline);
+    if (base::FeatureList::IsEnabled(
+            blink::features::kBlinkHeapConcurrentMarking)) {
+      is_tracing_done_ =
+          thread_state_->ConcurrentMarkingStep() && is_tracing_done_;
+    }
     return is_tracing_done_;
   }
   thread_state_->AtomicPauseMarkTransitiveClosure();