Revert of Remove applyAuthorStyles flag from ShadowRoot. (https://codereview.chromium.org/215313003/)

Reason for revert:
w3c/web-platform-tests/shadow-dom/elements-and-dom-objects/shadowroot-object/shadowroot-attributes/test-004.html started to fail.

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=w3c/web-platform-tests/shadow-dom/elements-and-dom-objects/shadowroot-object/shadowroot-attributes/test-004.html


Original issue's description:
> Remove applyAuthorStyles flag from ShadowRoot.
> 
> This re-applies https://src.chromium.org/viewvc/blink?revision=165673&view=revision.
> 
> BUG=357151
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170271

TBR=esprehn@chromium.org,tasak@google.com,hayato@chromium.org,dglazkov@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=357151

Review URL: https://codereview.chromium.org/216543002

git-svn-id: svn://svn.chromium.org/blink/trunk@170289 bbb929c8-8fbe-4397-9dbb-9b2b20218538