Decouple root visitors from object visitors.

src/profiler/heap-snapshot-generator.h

 // Copyright 2013 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.
 
 #ifndef V8_PROFILER_HEAP_SNAPSHOT_GENERATOR_H_
 #define V8_PROFILER_HEAP_SNAPSHOT_GENERATOR_H_
 
 #include <deque>
 #include <unordered_map>
 
 #include "include/v8-profiler.h"
 #include "src/base/platform/time.h"
 #include "src/objects.h"
 #include "src/profiler/strings-storage.h"
+#include "src/visitors.h"
 
 namespace v8 {
 namespace internal {
 
 class AllocationTracker;
 class AllocationTraceNode;
 class HeapEntry;
 class HeapIterator;
 class HeapProfiler;
 class HeapSnapshot;
@@ skipping 597 matching lines @@
   friend class HeapSnapshotJSONSerializerIterator;
 
   DISALLOW_COPY_AND_ASSIGN(HeapSnapshotJSONSerializer);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PROFILER_HEAP_SNAPSHOT_GENERATOR_H_