Revert "Revert "Implement Element.matches(selectors)""

This re-lands <https://codereview.chromium.org/106983004>, which was
reverted in <https://codereview.chromium.org/103303005>.

The root bug causing the revert was fixed in Polymer in
<https://github.com/Polymer/ShadowDOM/pull/332> and reached Chromium in
<https://codereview.chromium.org/98583008>.

BUG=326652

Review URL: https://codereview.chromium.org/133643006

git-svn-id: svn://svn.chromium.org/blink/trunk@164970 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make arguments to Element methods non-optional (except setAttribute)

This partially re-lands <https://codereview.chromium.org/105883012/>,
which was reverted in <https://codereview.chromium.org/120373003> because
making the second argument to setAttribute broke Twitter.

The second argument to setAttribute is left optional, making it
non-optional will be attempted again separately.

BUG=325922

Review URL: https://codereview.chromium.org/133683004

git-svn-id: svn://svn.chromium.org/blink/trunk@164971 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark media/W3C/video/events/event_order_loadstart_progress.html as flaky

TBR=tdanderson
BUG=333880

Review URL: https://codereview.chromium.org/136753003

git-svn-id: svn://svn.chromium.org/blink/trunk@164972 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[DevTools] Always show context menu for console messages.

On Mac, on right-click first text is selected under cursor
and then contextmenu handler fire with selection already set. That made
context menu very hard to use in console for Mac users.

BUG=330159

Review URL: https://codereview.chromium.org/117553004

git-svn-id: svn://svn.chromium.org/blink/trunk@164973 bbb929c8-8fbe-4397-9dbb-9b2b20218538
This patch rolls CodeMirror and all its plugins to v3.20. The new
version of css mode changed its internal name from 'css-base' to
just 'css', which implied changes in CodeMirrorUtils.js file.

NB: headlesscodemirror.js if not taken from v3.20 distribution as it has bugs; it's fixed version could be
found here: https://github.com/aslushnikov/CodeMirror/blob/925130e8b455c137b385c611a67dcb7d582c0281/addon/runmode/runmode-standalone.js

R=apavlov@chromium.org

Review URL: https://codereview.chromium.org/136433002

git-svn-id: svn://svn.chromium.org/blink/trunk@164974 bbb929c8-8fbe-4397-9dbb-9b2b20218538
A bunch of inspector editing tests are flaky on Windows

BUG=333882
TBR=tdanderson

Review URL: https://codereview.chromium.org/136803003

git-svn-id: svn://svn.chromium.org/blink/trunk@164975 bbb929c8-8fbe-4397-9dbb-9b2b20218538