Add a flag for memory reducer.

src/heap/memory-reducer.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 "src/heap/memory-reducer.h"
 
 #include "src/flags.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/heap-inl.h"
 #include "src/utils.h"
@@ skipping 132 matching lines @@
 
 bool MemoryReducer::WatchdogGC(const State& state, const Event& event) {
   return state.last_gc_time_ms != 0 &&
          event.time_ms > state.last_gc_time_ms + kWatchdogDelayMs;
 }
 
 
 // For specification of this function see the comment for MemoryReducer class.
 MemoryReducer::State MemoryReducer::Step(const State& state,
                                          const Event& event) {
-  if (!FLAG_incremental_marking) {
+  if (!FLAG_incremental_marking || !FLAG_memory_reducer) {
     return State(kDone, 0, 0, state.last_gc_time_ms);
   }
   switch (state.action) {
     case kDone:
       if (event.type == kTimer || event.type == kBackgroundIdleNotification) {
         return state;
       } else {
         DCHECK(event.type == kContextDisposed || event.type == kMarkCompact);
         return State(
             kWait, 0, event.time_ms + kLongDelayMs,
@@ skipping 56 matching lines @@
   auto timer_task = new MemoryReducer::TimerTask(this);
   V8::GetCurrentPlatform()->CallDelayedOnForegroundThread(
       isolate, timer_task, (delay_ms + kSlackMs) / 1000.0);
 }
 
 
 void MemoryReducer::TearDown() { state_ = State(kDone, 0, 0, 0.0); }
 
 }  // namespace internal
 }  // namespace v8