Delete some dead code.

tools/imagediff/image_diff_png.cc

 // Copyright 2013 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 "tools/imagediff/image_diff_png.h"
 
 #include <stdlib.h>
 #include <string.h>
 
 #include "base/logging.h"
@@ skipping 19 matching lines @@
   // This is the default Windows DIB order.
   FORMAT_BGRA,
 
   // 4 bytes per pixel, in pre-multiplied kARGB_8888_Config format. For use
   // with directly writing to a skia bitmap.
   FORMAT_SkBitmap
 };
 
 // Represents a comment in the tEXt ancillary chunk of the png.
 struct Comment {
-  Comment(const std::string& k, const std::string& t)
-    : key(k), text(t) {
-  }
-
-  ~Comment() {
-  };
-
   std::string key;
   std::string text;
 };
 
 // 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];
     unsigned char* pixel_out = &output[x * 4];
@@ skipping 584 matching lines @@
                    int height,
                    int row_byte_width,
                    bool discard_transparency,
                    std::vector<unsigned char>* output) {
   return Encode(input, FORMAT_BGRA,
       width, height, row_byte_width, discard_transparency,
       std::vector<Comment>(), output);
 }
 
 }  // image_diff_png