Update the tcmalloc vendor branch to r144 (gperftools 2.0).

third_party/tcmalloc/vendor/src/thread_cache.h

Index: third_party/tcmalloc/vendor/src/thread_cache.h
diff --git a/third_party/tcmalloc/vendor/src/thread_cache.h b/third_party/tcmalloc/vendor/src/thread_cache.h
index 1742d5ba54e57fad4fea8e1612f7ce4a83be29f9..1d0413b2a8a1dc712defa76ae103eea9ff011209 100644
--- a/third_party/tcmalloc/vendor/src/thread_cache.h
+++ b/third_party/tcmalloc/vendor/src/thread_cache.h
@@ -94,7 +94,6 @@ class ThreadCache {
   void Deallocate(void* ptr, size_t size_class);
 
   void Scavenge();
-  void Print(TCMalloc_Printer* out) const;
 
   int GetSamplePeriod();
 
@@ -120,10 +119,6 @@ class ThreadCache {
   // REQUIRES: Static::pageheap_lock is held.
   static void GetThreadStats(uint64_t* total_bytes, uint64_t* class_count);
 
-  // Write debugging statistics to 'out'.
-  // REQUIRES: Static::pageheap_lock is held.
-  static void PrintThreads(TCMalloc_Printer* out);
-
   // Sets the total thread cache size to new_size, recomputing the
   // individual thread cache sizes as necessary.
   // REQUIRES: Static::pageheap lock is held.
@@ -209,6 +204,10 @@ class ThreadCache {
       return SLL_Pop(&list_);
     }
 
+    void* Next() {
+      return SLL_Next(&list_);
+    }
+
     void PushRange(int N, void *start, void *end) {
       SLL_PushRange(&list_, start, end);
       length_ += N;
@@ -349,6 +348,12 @@ inline void ThreadCache::Deallocate(void* ptr, size_t cl) {
   FreeList* list = &list_[cl];
   size_ += Static::sizemap()->ByteSizeForClass(cl);
   ssize_t size_headroom = max_size_ - size_ - 1;
+
+  // This catches back-to-back frees of allocs in the same size
+  // class. A more comprehensive (and expensive) test would be to walk
+  // the entire freelist. But this might be enough to find some bugs.
+  ASSERT(ptr != list->Next());
+
   list->Push(ptr);
   ssize_t list_headroom =
       static_cast<ssize_t>(list->max_length()) - list->length();