optimize-ico-files: Automatically rebuild the AND mask of 32-bit images.

chrome/app/theme/README

 PNG Images
 ==========
 
 Please run src/tools/resources/optimize-png-files.sh on all new icons. For example:
   tools/resources/optimize-png-files.sh -o2 new_pngs_dir
 
 If this script does not work for some reason, at least pngcrush the files:
   mkdir crushed
   pngcrush -d crushed -brute -reduce -rem alla new/*.png
 
 ICO Images
 ==========
 
 Windows ICO icons should be in the following format:
 
 * A square image of each size: 256, 48, 32, 16.
 * The 256 image should be in PNG format, and optimized.
 * The smaller images should be in BMP (uncompressed) format.
 * Each of the smaller images (48 and less) should have an 8-bit and 32-bit
   version.
 * The 256 image should not be last (there is a bug in Gnome on Linux where icons
   look corrupted if the PNG image is last).
 
 If you are creating an ICO from a set of PNGs of different sizes, the following
 process (using ImageMagick and GIMP) satisfies the above conditions:
 
-**IMPORTANT**: There is an issue with GIMP generating sub-optimal ICO files
-(see http://crbug.com/526622#c35); therefore if you are creating or updating
-icons using the below process, please add mgiuca@chromium.org as a reviewer.
-TODO(mgiuca): Update the tools/process to work around the problem.
-
 1. Convert each of the smaller images to 8-bit. With ImageMagick:
 
     for f in FILENAME-??.png; \
         do convert $f -dither None -colors 256 \
             png8:`basename $f .png`-indexed.png; \
     done
 
 2. Combine the images into an ICO file. With ImageMagick:
 
     convert FILENAME-256.png FILENAME-{48,32,16}{-indexed,}.png FILENAME.ico
 
 3. Unfortunately, the 8-bit images have been converted back into 32-bit images.
    Open the icon in GIMP and re-export it. This will also convert the large
    256 image into a compressed PNG.
 4. Run src/tools/resources/optimize-ico-files.py on the resulting .ico file.
 
 You can also run src/tools/resources/optimize-ico-files.py on existing .ico
-files. This will run a basic PNG optimization pass.
+files. This will run a basic PNG optimization pass and fix up any broken image
+masks (http://crbug.com/534679).