HeapCompact doesn't need to support multiple threads

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

Index: third_party/WebKit/Source/platform/heap/HeapCompact.h
diff --git a/third_party/WebKit/Source/platform/heap/HeapCompact.h b/third_party/WebKit/Source/platform/heap/HeapCompact.h
index e7e13334f1097d7ccef34eac2d4bf84f8f20f3e2..5c8e1a880b349dd87510a280753adeadfd891043 100644
--- a/third_party/WebKit/Source/platform/heap/HeapCompact.h
+++ b/third_party/WebKit/Source/platform/heap/HeapCompact.h
@@ -139,18 +139,6 @@ class PLATFORM_EXPORT HeapCompact final {
   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;