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

src/heap/heap.cc

 // Copyright 2012 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 "src/heap/heap.h"
 
 #include <unordered_map>
 #include <unordered_set>
 
 #include "src/accessors.h"
@@ skipping 5526 matching lines @@
 }
 
 // This function returns either kNoLimit, kSoftLimit, or kHardLimit.
 // The kNoLimit means that either incremental marking is disabled or it is too
 // early to start incremental marking.
 // The kSoftLimit means that incremental marking should be started soon.
 // The kHardLimit means that incremental marking should be started immediately.
 Heap::IncrementalMarkingLimit Heap::IncrementalMarkingLimitReached() {
   // Code using an AlwaysAllocateScope assumes that the GC state does not
   // change; that implies that no marking steps must be performed.
-  if (!incremental_marking()->CanBeActivated() || always_allocate() ||
-      PromotedSpaceSizeOfObjects() <=
-          IncrementalMarking::kActivationThreshold) {
+  if (!incremental_marking()->CanBeActivated() || always_allocate()) {
     // Incremental marking is disabled or it is too early to start.
     return IncrementalMarkingLimit::kNoLimit;
   }
+  if (FLAG_stress_incremental_marking) {
+    return IncrementalMarkingLimit::kHardLimit;
+  }
+  if (PromotedSpaceSizeOfObjects() <=
+      IncrementalMarking::kActivationThreshold) {
+    // Incremental marking is disabled or it is too early to start.
+    return IncrementalMarkingLimit::kNoLimit;
+  }
   if ((FLAG_stress_compaction && (gc_count_ & 1) != 0) ||
       HighMemoryPressure()) {
     // If there is high memory pressure or stress testing is enabled, then
     // start marking immediately.
     return IncrementalMarkingLimit::kHardLimit;
   }
   size_t old_generation_space_available = OldGenerationSpaceAvailable();
   if (old_generation_space_available > new_space_->Capacity()) {
     return IncrementalMarkingLimit::kNoLimit;
   }
@@ skipping 1009 matching lines @@
     case LO_SPACE:
       return "LO_SPACE";
     default:
       UNREACHABLE();
   }
   return NULL;
 }
 
 }  // namespace internal
 }  // namespace v8