ui/gfx: optimize RGBA to RGB conversion by using memcpy in png_codec.cc

ui/gfx/codec/png_codec.cc

 // Copyright (c) 2012 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.
 
 #include "ui/gfx/codec/png_codec.h"
 
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 #include "third_party/libpng/png.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ skipping 15 matching lines @@
     unsigned char* pixel_out = &output[x * 4];
     pixel_out[0] = pixel_in[2];
     pixel_out[1] = pixel_in[1];
     pixel_out[2] = pixel_in[0];
     pixel_out[3] = pixel_in[3];
   }
 }
 
 void ConvertRGBAtoRGB(const unsigned char* rgba, int pixel_width,
                       unsigned char* rgb, bool* is_opaque) {
-  for (int x = 0; x < pixel_width; x++) {
-    const unsigned char* pixel_in = &rgba[x * 4];
-    unsigned char* pixel_out = &rgb[x * 3];
-    pixel_out[0] = pixel_in[0];
-    pixel_out[1] = pixel_in[1];
-    pixel_out[2] = pixel_in[2];
-  }
+  for (int x = 0; x < pixel_width; x++)
+    memcpy(&rgb[x * 3], &rgba[x * 4], 3);
 }
 
 void ConvertSkiatoRGB(const unsigned char* skia, int pixel_width,
                       unsigned char* rgb, bool* is_opaque) {
   for (int x = 0; x < pixel_width; x++) {
     const uint32_t pixel_in = *reinterpret_cast<const uint32_t*>(&skia[x * 4]);
     unsigned char* pixel_out = &rgb[x * 3];
 
     int alpha = SkGetPackedA32(pixel_in);
     if (alpha != 0 && alpha != 255) {
@@ skipping 753 matching lines @@
 }
 
 PNGCodec::Comment::Comment(const std::string& k, const std::string& t)
     : key(k), text(t) {
 }
 
 PNGCodec::Comment::~Comment() {
 }
 
 }  // namespace gfx