Fullscreen videos shouldn't be affected by CSS left/top properties

This fixes a regression introduced in
https://chromiumcodereview.appspot.com/22454003 which added position:relative
to fullscreen videos to force stacking context. It was previously statically
positioned to ignore top/left properties. This CL adds left:0 and top:0 to
override any user-supplied top/left properties.

BUG=315540

Review URL: https://codereview.chromium.org/149773007

git-svn-id: svn://svn.chromium.org/blink/trunk@167073 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove old NeedsManualRebaseline

R=jochen@chromium.org

NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/163063002

git-svn-id: svn://svn.chromium.org/blink/trunk@167074 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert of Remove applyAuthorStyles flag from ShadowRoot. (https://codereview.chromium.org/143993006)

It turned out that Quickoffice doesn't have workarounds because shadow
combinators, which were expected to be workarounds, are available only when the
Experimental Web Platform Features flag turned on,

We should put applyAuthorStyles back for M34 temporary.  We'll drop
applyAuthorStyles after we have shadow combinators enabled in default.  I assume these
things will happen in M35.

This revert patch is also adding deprecation warning messages to the usage of
ShadowRoot.applyAuthorStyles.

BUG=342622

Review URL: https://codereview.chromium.org/162563002

git-svn-id: svn://svn.chromium.org/blink/trunk@167075 bbb929c8-8fbe-4397-9dbb-9b2b20218538