HeapCompact doesn't need to support multiple threads

third_party/WebKit/Source/platform/heap/HeapCompact.h

 // Copyright 2016 The Chromium 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 HeapCompact_h
 #define HeapCompact_h
 
 #include "platform/PlatformExport.h"
 #include "platform/heap/BlinkGC.h"
 #include "wtf/DataLog.h"
@@ skipping 121 matching lines @@
   static const size_t kFreeListSizeThreshold = 512 * 1024;
 
   MovableObjectFixups& fixups();
 
   std::unique_ptr<MovableObjectFixups> m_fixups;
 
   // Set to |true| when a compacting sweep will go ahead.
   bool m_doCompact;
   size_t m_gcCountSinceLastCompaction;
 
-  // Lock protecting finishedThreadCompaction() signalling.
-  Mutex m_mutex;
-
-  // All threads performing a GC must synchronize on completion
-  // of all heap compactions. Not doing so risks one thread resuming
-  // the mutator, which could perform cross-thread access to a heap
-  // that's still in the process of being compacted.
-  ThreadCondition m_finished;
-
-  // Number of heap threads participating in the compaction.
-  int m_threadCount;
-
   // Last reported freelist size, across all compactable arenas.
   size_t m_freeListSize;
 
   // If compacting, i'th heap arena will be compacted
   // if corresponding bit is set. Indexes are in
   // the range of BlinkGC::ArenaIndices.
   unsigned m_compactableArenas;
 
   // Stats, number of (complete) pages freed/decommitted +
   // bytes freed (which will include partial pages.)
@@ skipping 32 matching lines @@
 #if DEBUG_HEAP_FREELIST == 2
 #define LOG_HEAP_FREELIST_VERBOSE(msg, ...) \
   LOG_HEAP_COMPACTION_INTERNAL(msg, ##__VA_ARGS__)
 #else
 #define LOG_HEAP_FREELIST_VERBOSE(msg, ...) \
   do {                                      \
   } while (0)
 #endif
 
 #endif  // HeapCompact_h