Add a script to extract used resource ids.

Script extracts resource IDs from the build output for the resources
that cause an "unknown pragma" warning.

BUG=338759
R=newt@chromium.org

Review URL: https://codereview.chromium.org/195513003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256409 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256409