heap: Minor marking tweaks

1) Traces show that it can take a relatively long time before Oilpan
   starts flushing v8 references (e.g. ~10 steps spent just on the
   bailout worklist). This CL moves v8 references flushing before
   processing of the bailout worklist.
2) Traces also show that a shorter duration for the first marking step
   can suffice.

Bug: 986235
Change-Id: If7bad026e91f1fdf1899035bda049834e7bffab5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339356
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795059}

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

@@ -388,6 +388,15 @@ bool ThreadHeap::AdvanceMarking(MarkingVisitor* visitor,
       // Start with mutator-thread-only worklists (not fully constructed).
       // If time runs out, concurrent markers can take care of the rest.
 
+      {
+        ThreadHeapStatsCollector::EnabledScope inner_scope(
+            stats_collector(),
+            ThreadHeapStatsCollector::kMarkFlushV8References);
+        finished = FlushV8References(deadline);
+        if (!finished)
+          break;
+      }
+
       {
         ThreadHeapStatsCollector::EnabledScope inner_scope(
             stats_collector(), ThreadHeapStatsCollector::kMarkBailOutObjects);
@@ -407,15 +416,6 @@ bool ThreadHeap::AdvanceMarking(MarkingVisitor* visitor,
           break;
       }
 
-      {
-        ThreadHeapStatsCollector::EnabledScope inner_scope(
-            stats_collector(),
-            ThreadHeapStatsCollector::kMarkFlushV8References);
-        finished = FlushV8References(deadline);
-        if (!finished)
-          break;
-      }
-
       {
         ThreadHeapStatsCollector::EnabledScope inner_scope(
             stats_collector(),

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

@@ -19,7 +19,7 @@ class PLATFORM_EXPORT MarkingSchedulingOracle {
   // Duration of one incremental marking step. Should be short enough that it
   // doesn't cause jank even though it is scheduled as a normal task.
   static constexpr base::TimeDelta kDefaultIncrementalMarkingStepDuration =
-      base::TimeDelta::FromMillisecondsD(0.5);
+      base::TimeDelta::FromMillisecondsD(0.1);
 
   // Minimum number of bytes that should be marked during an incremental
   // marking step.