Re-apply Remove applyAuthorStyles flag from ShadowRoot. (https://codereview.chromium.org/215313003/)"

A triple-revert to rea-pply https://src.chromium.org/viewvc/blink?revision=165673&view=revision.

BUG=357151
TBR=tkent

Review URL: https://codereview.chromium.org/216383005

git-svn-id: svn://svn.chromium.org/blink/trunk@170352 bbb929c8-8fbe-4397-9dbb-9b2b20218538