Fix invalid use of int in Zone.

src/compiler.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_COMPILER_H_
 #define V8_COMPILER_H_
 
 #include "src/allocation.h"
 #include "src/ast.h"
 #include "src/bailout-reason.h"
@@ skipping 755 matching lines @@
 
   const char* name() const { return name_; }
   CompilationInfo* info() const { return info_; }
   Isolate* isolate() const { return info()->isolate(); }
   Zone* zone() { return &zone_; }
 
  private:
   const char* name_;
   CompilationInfo* info_;
   Zone zone_;
-  unsigned info_zone_start_allocation_size_;
+  size_t info_zone_start_allocation_size_;
   base::ElapsedTimer timer_;
 
   DISALLOW_COPY_AND_ASSIGN(CompilationPhase);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_COMPILER_H_