ui: Add RGBX_8888 buffer format.

ui/gfx/buffer_types.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_GFX_BUFFER_TYPES_H_
 #define UI_GFX_BUFFER_TYPES_H_
 
 namespace gfx {
 
 // The format needs to be taken into account when mapping a buffer into the
 // client's address space.
 enum class BufferFormat {
   ATC,
   ATCIA,
   DXT1,
   DXT5,
   ETC1,
   R_8,
   RGBA_4444,
+  RGBX_8888,
   RGBA_8888,
   BGRX_8888,
   BGRA_8888,
   YUV_420,
   YUV_420_BIPLANAR,
   UYVY_422,
 
   LAST = UYVY_422
 };
 
 // The usage mode affects how a buffer can be used. Only buffers created with
 // MAP can be mapped into the client's address space and accessed by the CPU.
 // PERSISTENT_MAP adds the additional condition that successive Map() calls
 // (with Unmap() calls between) will return a pointer to the same memory
 // contents.
 enum class BufferUsage { MAP, PERSISTENT_MAP, SCANOUT, LAST = SCANOUT };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_BUFFER_TYPES_H_