Adds asynchronous unzip functions to ZipReader

Updates ImageWriterPrivate to use the new asynchronous functions.

BUG=324091

Review URL: https://codereview.chromium.org/92873003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245393 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245393