Remove scoped styles (retry)

Removes <style scoped>.

This was discussed and approved with LGTMs in blink-dev:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/R1x18ZLS5qQ/Bjuh_cENhlQJ

Chrome status dashboard entry:
http://www.chromestatus.com/features/5374137958662144

The previous one failed to land due to stale generated file issues and browser test failures (3 times):
https://codereview.chromium.org/310443002/ (original CL)
http://crrev.com/175550 -> http://crrev.com/175552 (stale generated file issue)
http://crrev.com/175555 -> http://crrev.com/175561 (stale generated file issue)
http://crrev.com/175720 -> http://crrev.com/175754 (browser test failures)

Browser test failure was due to HTMLStyleElement refcounting mismatch
in ShadowRoot.  This CL fixes the issue and adds a layout test
fast/css/shadow-style-removed-out-of-document.html
to catch the condition.

Note:
This is based on esprehn's original cl:
https://codereview.chromium.org/214693002/

BUG=379096
TEST=pass all layout tests and do not break any existing tests

Review URL: https://codereview.chromium.org/325663003

git-svn-id: svn://svn.chromium.org/blink/trunk@175993 bbb929c8-8fbe-4397-9dbb-9b2b20218538