"fetch android" is a basic alias for "fetch chromium --target_os=android",
which adds "target_os=['android']" to the gclient specs as described in
chromium's AndroidBuildInstructions wiki page.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/14315010

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@197031 0039d316-1c4b-4281-b951-d872f2087c98