Add a PNGEncoder helper function that takes an SkBitmap,

base/gfx/png_encoder.cc

Index: base/gfx/png_encoder.cc
diff --git a/base/gfx/png_encoder.cc b/base/gfx/png_encoder.cc
old mode 100644
new mode 100755
index 7b44a5259867babfd88750acc40f2be593436182..64e46d7c16ee286782f9f3836d5e6391863fd966
--- a/base/gfx/png_encoder.cc
+++ b/base/gfx/png_encoder.cc
@@ -5,6 +5,7 @@
 #include "base/basictypes.h"
 #include "base/gfx/png_encoder.h"
 #include "base/logging.h"
+#include "skia/include/SkBitmap.h"
 
 extern "C" {
 #include "png.h"
@@ -191,3 +192,14 @@ bool PNGEncoder::Encode(const unsigned char* input, ColorFormat format,
   return true;
 }
 
+// static
+bool PNGEncoder::EncodeBGRASkBitmap(const SkBitmap& input,
+                                    bool discard_transparency,
+                                    std::vector<unsigned char>* output) {
+  SkAutoLockPixels input_lock(input);
+  DCHECK_EQ(input.bytesPerPixel(), 4);
+  return Encode(static_cast<unsigned char*>(input.getPixels()),
+                PNGEncoder::FORMAT_BGRA, input.width(), input.height(),
+                input.rowBytes(), discard_transparency, output);
+}
+