Remove applyAuthorStyles flag from ShadowRoot.

This re-applies https://src.chromium.org/viewvc/blink?revision=165673&view=revision.

BUG=357151

Review URL: https://codereview.chromium.org/215313003

git-svn-id: svn://svn.chromium.org/blink/trunk@170271 bbb929c8-8fbe-4397-9dbb-9b2b20218538