Remove NoColorMatchException so eliminate exception being caught running VM in checked mode.

BUG=

Review URL: https://chromiumcodereview.appspot.com//14843011
Merge branch 'master' of https://github.com/dart-lang/csslib into new_css
version 0.4.6+5

BUG=

Review URL: https://chromiumcodereview.appspot.com//15039019
Merge branch 'master' of https://github.com/dart-lang/csslib into new_css
Integrated CL comments