Implementation of brand-color

Add APIs
- WebFrame::brandColor() to get the brand color.
- WebFrameClinet::didChangeBrandColor to notify the brand color change.

BUG=383941

Intent to implement and ship link
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/nzRY-h_-_ig

Review URL: https://codereview.chromium.org/329943004

git-svn-id: svn://svn.chromium.org/blink/trunk@176142 bbb929c8-8fbe-4397-9dbb-9b2b20218538