gfx: Use unsigned strides for gpu memory buffers.

ui/ozone/public/client_native_pixmap.h

 // Copyright 2015 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 UI_OZONE_PUBLIC_CLIENT_NATIVE_PIXMAP_H_
 #define UI_OZONE_PUBLIC_CLIENT_NATIVE_PIXMAP_H_
 
 #include "ui/ozone/ozone_export.h"
 
 namespace ui {
 
 // This represents a buffer that can be written to directly by regular CPU code,
 // but can also be read by the GPU.
 // NativePixmap is its counterpart in GPU process.
 class OZONE_EXPORT ClientNativePixmap {
  public:
   virtual ~ClientNativePixmap() {}
 
   virtual void* Map() = 0;
   virtual void Unmap() = 0;
-  virtual void GetStride(int* stride) const = 0;
+  virtual void GetStride(uint32_t* stride) const = 0;
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PUBLIC_CLIENT_NATIVE_PIXMAP_H_