DevTools: CSS outline dialog to use front-end css tokenizer

This patch moves CSS outline dialog from using structural information
retrieved from protocol into using front-end tokenizers to parse
CSS content and build outline.

BUG=341506

Review URL: https://codereview.chromium.org/137383015

git-svn-id: svn://svn.chromium.org/blink/trunk@167007 bbb929c8-8fbe-4397-9dbb-9b2b20218538