Use a direct include of strings headers in ui/, part 3.

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/string_util.h"
+#include "base/strings/string_util.h"
+#include "third_party/libpng/png.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+#include "third_party/skia/include/core/SkColorPriv.h"
+#include "third_party/skia/include/core/SkUnPreMultiply.h"
+#include "third_party/zlib/zlib.h"
 #include "ui/gfx/size.h"
 #include "ui/gfx/skia_util.h"
-#include "third_party/libpng/png.h"
-#include "third_party/skia/include/core/SkBitmap.h"
-#include "third_party/skia/include/core/SkUnPreMultiply.h"
-#include "third_party/skia/include/core/SkColorPriv.h"
-#include "third_party/zlib/zlib.h"
 
 namespace gfx {
 
 namespace {
 
 // Converts BGRA->RGBA and RGBA->BGRA.
 void ConvertBetweenBGRAandRGBA(const unsigned char* input, int pixel_width,
                                unsigned char* output, bool* is_opaque) {
   for (int x = 0; x < pixel_width; x++) {
     const unsigned char* pixel_in = &input[x * 4];
@@ skipping 751 matching lines @@
 }
 
 PNGCodec::Comment::Comment(const std::string& k, const std::string& t)
     : key(k), text(t) {
 }
 
 PNGCodec::Comment::~Comment() {
 }
 
 }  // namespace gfx