Add a PNGEncoder helper function that takes an SkBitmap,

base/gfx/png_encoder.h

 // Copyright (c) 2006-2008 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 BASE_GFX_PNG_ENCODER_H__
 #define BASE_GFX_PNG_ENCODER_H__
 
 #include <vector>
 
 #include "base/basictypes.h"
 
+class SkBitmap;
+
 // Interface for encoding PNG data. This is a wrapper around libpng,
 // which has an inconvenient interface for callers. This is currently designed
 // for use in tests only (where we control the files), so the handling isn't as
 // robust as would be required for a browser (see Decode() for more).  WebKit
 // has its own more complicated PNG decoder which handles, among other things,
 // partially downloaded data.
 class PNGEncoder {
  public:
   enum ColorFormat {
     // 3 bytes per pixel (packed), in RGB order regardless of endianness.
@@ skipping 22 matching lines @@
   //   (often, each row is padded to the next machine word).
   // discard_transparency: when true, and when the input data format includes
   //   alpha values, these alpha values will be discarded and only RGB will be
   //   written to the resulting file. Otherwise, alpha values in the input
   //   will be preserved.
   static bool Encode(const unsigned char* input, ColorFormat format,
                      int w, int h, int row_byte_width,
                      bool discard_transparency,
                      std::vector<unsigned char>* output);
 
+  // Call PNGEncoder::Encode on the supplied SkBitmap |input|, which is assumed
+  // to be BGRA, 32 bits per pixel. The params |discard_transparency| and
+  // |output| are passed directly to Encode; refer to Encode for more
+  // information. During the call, an SkAutoLockPixels lock is held on |input|.
+  static bool EncodeBGRASkBitmap(const SkBitmap& input,
+                                 bool discard_transparency,
+                                 std::vector<unsigned char>* output);
+
  private:
   DISALLOW_EVIL_CONSTRUCTORS(PNGEncoder);
 };
 
 #endif  // BASE_GFX_PNG_ENCODER_H__