CSS shapes support in Web Inspector

Highlights the shape outside element when selected in web inspector:
- Compute shape information to display in inspector overlay canvas
- Path is computed based on ShapeOutsideInfo.
- In Inspector view only highlighted shape and margin are shown, no quad node is highlighted. 

R=jochen@chromium.org, betravis@adobe.com
BUG=351441
TEST=Different shapes tests in the web inspector

Review URL: https://codereview.chromium.org/237313003

git-svn-id: svn://svn.chromium.org/blink/trunk@173379 bbb929c8-8fbe-4397-9dbb-9b2b20218538