Adapt upstream patches fixing potential deadlock in tcmalloc after fork.

third_party/tcmalloc/chromium/src/central_freelist.h

 // Copyright (c) 2008, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 61 matching lines @@
 
   // Returns the number of free objects in the transfer cache.
   int tc_length();
 
   // Returns the memory overhead (internal fragmentation) attributable
   // to the freelist.  This is memory lost when the size of elements
   // in a freelist doesn't exactly divide the page-size (an 8192-byte
   // page full of 5-byte objects would have 2 bytes memory overhead).
   size_t OverheadBytes();
 
+  // Lock/Unlock the internal SpinLock. Used on the pthread_atfork call
+  // to set the lock in a consistent state before the fork.
+  void Lock() {
+    lock_.Lock();
+  }
+
+  void Unlock() {
+    lock_.Unlock();
+  }
+
  private:
   // TransferCache is used to cache transfers of
   // sizemap.num_objects_to_move(size_class) back and forth between
   // thread caches and the central cache for a given size class.
   struct TCEntry {
     void *head;  // Head of chain of objects.
     void *tail;  // Tail of chain of objects.
   };
 
   // A central cache freelist can have anywhere from 0 to kMaxNumTransferEntries
@@ skipping 99 matching lines @@
 class CentralFreeListPaddedTo<0> : public CentralFreeList {
 };
 
 class CentralFreeListPadded : public CentralFreeListPaddedTo<
   sizeof(CentralFreeList) % 64> {
 };
 
 }  // namespace tcmalloc
 
 #endif  // TCMALLOC_CENTRAL_FREELIST_H_