[heap] Allow pausing incremental steps

Bug: 843903
Change-Id: I51f920f3e775e09ebb8b1dcc569f229b1c98c678
Reviewed-on: https://chromium-review.googlesource.com/c/1280662Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599621}

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

@@ -834,6 +834,7 @@ void UnexpectedGCState(ThreadState::GCState gc_state) {
     UNEXPECTED_GCSTATE(kIdleGCScheduled);
     UNEXPECTED_GCSTATE(kPreciseGCScheduled);
     UNEXPECTED_GCSTATE(kFullGCScheduled);
+    UNEXPECTED_GCSTATE(kIncrementalMarkingStepPaused);
     UNEXPECTED_GCSTATE(kIncrementalMarkingStepScheduled);
     UNEXPECTED_GCSTATE(kIncrementalMarkingFinalizeScheduled);
     UNEXPECTED_GCSTATE(kPageNavigationGCScheduled);
@@ -857,6 +858,7 @@ void ThreadState::SetGCState(GCState gc_state) {
           gc_state_ == kNoGCScheduled || gc_state_ == kIdleGCScheduled ||
           gc_state_ == kPreciseGCScheduled || gc_state_ == kFullGCScheduled ||
           gc_state_ == kPageNavigationGCScheduled ||
+          gc_state_ == kIncrementalMarkingStepPaused ||
           gc_state_ == kIncrementalMarkingStepScheduled ||
           gc_state_ == kIncrementalMarkingFinalizeScheduled ||
           gc_state_ == kIncrementalGCScheduled);
@@ -879,6 +881,7 @@ void ThreadState::SetGCState(GCState gc_state) {
       DCHECK(!IsSweepingInProgress());
       VERIFY_STATE_TRANSITION(
           gc_state_ == kNoGCScheduled || gc_state_ == kIdleGCScheduled ||
+          gc_state_ == kIncrementalMarkingStepPaused ||
           gc_state_ == kIncrementalMarkingStepScheduled ||
           gc_state_ == kIncrementalMarkingFinalizeScheduled ||
           gc_state_ == kPreciseGCScheduled || gc_state_ == kFullGCScheduled ||
@@ -898,6 +901,12 @@ void ThreadState::SetGCState(GCState gc_state) {
       VERIFY_STATE_TRANSITION(gc_state_ == kNoGCScheduled ||
                               gc_state_ == kIdleGCScheduled);
       break;
+    case kIncrementalMarkingStepPaused:
+      DCHECK(CheckThread());
+      DCHECK(IsMarkingInProgress());
+      DCHECK(!IsSweepingInProgress());
+      VERIFY_STATE_TRANSITION(gc_state_ == kIncrementalMarkingStepScheduled);
+      break;
     default:
       NOTREACHED();
   }
@@ -1484,7 +1493,7 @@ void ThreadState::IncrementalMarkingStep() {
       // further marking if new objects are discovered. Otherwise, just process
       // the rest in the atomic pause.
       DCHECK(IsUnifiedGCMarkingInProgress());
-      SetGCState(kNoGCScheduled);
+      SetGCState(kIncrementalMarkingStepPaused);
     } else {
       ScheduleIncrementalMarkingFinalize();
     }

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

@@ -147,6 +147,7 @@ class PLATFORM_EXPORT ThreadState final
   enum GCState {
     kNoGCScheduled,
     kIdleGCScheduled,
+    kIncrementalMarkingStepPaused,
     kIncrementalMarkingStepScheduled,
     kIncrementalMarkingFinalizeScheduled,
     kPreciseGCScheduled,