Add template parameter and unittests to atomic utils.

src/heap/heap.h

 // Copyright 2012 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_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 2120 matching lines @@
 
   // For keeping track of how much data has survived
   // scavenge since last new space expansion.
   int survived_since_last_expansion_;
 
   // ... and since the last scavenge.
   int survived_last_scavenge_;
 
   // This is not the depth of nested AlwaysAllocateScope's but rather a single
   // count, as scopes can be acquired from multiple tasks (read: threads).
-  AtomicValue always_allocate_scope_count_;
+  AtomicValue<size_t> always_allocate_scope_count_;
 
   // For keeping track of context disposals.
   int contexts_disposed_;
 
   int global_ic_age_;
 
   int scan_on_scavenge_pages_;
 
   NewSpace new_space_;
   OldSpace* old_space_;
@@ skipping 594 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_