Fix invalid use of int in Zone.

src/lithium-allocator.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_LITHIUM_ALLOCATOR_H_
 #define V8_LITHIUM_ALLOCATOR_H_
 
 #include "src/v8.h"
 
 #include "src/allocation.h"
@@ skipping 546 matching lines @@
 };
 
 
 class LAllocatorPhase : public CompilationPhase {
  public:
   LAllocatorPhase(const char* name, LAllocator* allocator);
   ~LAllocatorPhase();
 
  private:
   LAllocator* allocator_;
-  unsigned allocator_zone_start_allocation_size_;
+  size_t allocator_zone_start_allocation_size_;
 
   DISALLOW_COPY_AND_ASSIGN(LAllocatorPhase);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_LITHIUM_ALLOCATOR_H_