[heap] Hide GCTracer inside the heap component.

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.h"
 #include "src/objects-inl.h"  // TODO(mstarzinger): Temporary cycle breaker!
 #include "src/utils.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace internal {
 
 const int MemoryReducer::kLongDelayMs = 5000;
 const int MemoryReducer::kShortDelayMs = 500;
@@ skipping 202 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); }
 
 }  // internal
 }  // v8