Convert CreateCdmBuffer() to use size_t for |capacity|

media/cdm/simple_cdm_allocator.h

 // Copyright 2016 The Chromium 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 MEDIA_CDM_SIMPLE_CDM_ALLOCATOR_H_
 #define MEDIA_CDM_SIMPLE_CDM_ALLOCATOR_H_
 
+#include <stddef.h>
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "media/cdm/cdm_allocator.h"
 
 namespace media {
 
 // This is a simple CdmAllocator for testing.
 class SimpleCdmAllocator : public CdmAllocator {
  public:
   SimpleCdmAllocator();
   ~SimpleCdmAllocator() final;
 
   // CdmAllocator implementation.
-  cdm::Buffer* CreateCdmBuffer(uint32_t capacity) final;
+  cdm::Buffer* CreateCdmBuffer(size_t capacity) final;
   scoped_ptr<VideoFrameImpl> CreateCdmVideoFrame() final;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SimpleCdmAllocator);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CDM_SIMPLE_CDM_ALLOCATOR_H_