Web Animations CSS: Add to experimental web platform features

This enables use of the Web Animations engine for CSS animations and
transitions when running with experimental web platform features enabled.

It also removes the existing web-animations-css virtual LayoutTests suite
(which ran with --enable-web-animations-css) and replaces it with a new
legacy-animations-engine virtual suite (which runs with
--disable-web-animations-css). Expected results are relocated appropriately.

The change in the expected results for the main animations/ and transitions/
directories document the behavioral progressions introduced by the switch to
the Web Animations engine.

R=dstockwell
BUG=258896, 322272

Review URL: https://codereview.chromium.org/70903004

git-svn-id: svn://svn.chromium.org/blink/trunk@162504 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Get rid of FrameSelection dependency from EditorClientImpl

This patch removes FrameSelection dependency from EditorClientImpl and removes Frame.h inclusion to reduce dependency for ease of maintenance and making compilation faster.

BUG=n/a
TEST=n/a; no behavior changes

Review URL: https://codereview.chromium.org/80373002

git-svn-id: svn://svn.chromium.org/blink/trunk@162505 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Tests and dead code removal after r162494

BUG=321550,319281

Review URL: https://codereview.chromium.org/82153002

git-svn-id: svn://svn.chromium.org/blink/trunk@162506 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add a test case that shows the amount of recalc we do we adding/removing stylesheets.

This is in preparation for reworking StyleSheetCollection::compareStyleSheets.

Review URL: https://codereview.chromium.org/82003002

git-svn-id: svn://svn.chromium.org/blink/trunk@162507 bbb929c8-8fbe-4397-9dbb-9b2b20218538