Compatibility patch to allow comments to be removed from base parser

This is an initial (Blink-side) compatibility CL so we can make changes
to the base parser in Chromium, notably (potentially) removing Comments.
For syncing reasons, this needs to land first, then in order:

2. (Chromium) Issue 21035003: Move Comments to PPAPI lexer & parser
https://codereview.chromium.org/21035003/

3. (Blink) Issue 21328003: Remove Comments from lexer and parser
https://codereview.chromium.org/21328003/

Review URL: https://chromiumcodereview.appspot.com/21199003

git-svn-id: svn://svn.chromium.org/blink/trunk@155291 bbb929c8-8fbe-4397-9dbb-9b2b20218538