[heap] Add --stress-incremental-marking flag.

test/cctest/heap/test-incremental-marking.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 
 #ifdef __linux__
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
@@ skipping 83 matching lines @@
     return dummy;
   }
 
  private:
   v8::Platform* platform_;
   Task* task_;
 };
 
 TEST(IncrementalMarkingUsingTasks) {
   if (!i::FLAG_incremental_marking) return;
+  FLAG_stress_incremental_marking = false;
   CcTest::InitializeVM();
   v8::Platform* old_platform = i::V8::GetCurrentPlatform();
   MockPlatform platform(old_platform);
   i::V8::SetPlatformForTesting(&platform);
   i::heap::SimulateFullSpace(CcTest::heap()->old_space());
   i::IncrementalMarking* marking = CcTest::heap()->incremental_marking();
   marking->Stop();
   marking->Start(i::GarbageCollectionReason::kTesting);
   CHECK(platform.PendingTask());
   while (platform.PendingTask()) {
     platform.PerformTask();
   }
   CHECK(marking->IsStopped());
   i::V8::SetPlatformForTesting(old_platform);
 }
 
 }  // namespace internal
 }  // namespace v8