Make Linux packaging options more granular.

This allows us to not waste time building packages/channels we don't care about. Also added option to build new 'trunk' channel packages, which are a special configuration for developer testing.

Review URL: http://codereview.chromium.org/418021


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@32879 0039d316-1c4b-4281-b951-d872f2087c98