cppgc: Fix compaction cancellation

Bug: chromium:1056170
Change-Id: I6b77c06b8c787a00be00b84490155588608c75da
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2764464Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73448}

src/heap/cppgc/compactor.cc

@@ -470,7 +470,6 @@ void Compactor::InitializeIfShouldCompact(
   compaction_worklists_ = std::make_unique<CompactionWorklists>();
 
   is_enabled_ = true;
-  enable_for_next_gc_for_testing_ = false;
 }
 
 bool Compactor::CancelIfShouldNotCompact(
@@ -506,9 +505,15 @@ Compactor::CompactableSpaceHandling Compactor::CompactSpacesIfEnabled() {
     CompactSpace(space, movable_references);
   }
 
+  enable_for_next_gc_for_testing_ = false;
   is_enabled_ = false;
   return CompactableSpaceHandling::kIgnore;
 }
 
+void Compactor::EnableForNextGCForTesting() {
+  DCHECK_NULL(heap_.heap()->marker());
+  enable_for_next_gc_for_testing_ = true;
+}
+
 }  // namespace internal
 }  // namespace cppgc

src/heap/cppgc/compactor.h

@@ -34,7 +34,7 @@ class V8_EXPORT_PRIVATE Compactor final {
     return compaction_worklists_.get();
   }
 
-  void EnableForNextGCForTesting() { enable_for_next_gc_for_testing_ = true; }
+  void EnableForNextGCForTesting();
   bool IsEnabledForTesting() const { return is_enabled_; }
 
  private:

test/unittests/heap/cppgc/compactor-unittest.cc

@@ -76,13 +76,6 @@ class CompactorTest : public testing::TestWithPlatform {
     EXPECT_TRUE(compactor().IsEnabledForTesting());
   }
 
-  void CancelCompaction() {
-    bool cancelled = compactor().CancelIfShouldNotCompact(
-        GarbageCollector::Config::MarkingType::kAtomic,
-        GarbageCollector::Config::StackState::kMayContainHeapPointers);
-    EXPECT_TRUE(cancelled);
-  }
-
   void FinishCompaction() { compactor().CompactSpacesIfEnabled(); }
 
   void StartGC() {
@@ -134,11 +127,6 @@ TEST_F(CompactorTest, NothingToCompact) {
   heap()->stats_collector()->NotifySweepingCompleted();
 }
 
-TEST_F(CompactorTest, CancelledNothingToCompact) {
-  StartCompaction();
-  CancelCompaction();
-}
-
 TEST_F(CompactorTest, NonEmptySpaceAllLive) {
   static constexpr int kNumObjects = 10;
   Persistent<CompactableHolder<kNumObjects>> holder =