Implement heuristic for showing media controls during playback w/o a mouse

This implements a heuristic that allows the media controls to re-appear
when playback has started and the mouse is unavailable.
The behavior is triggered by a 'focusin' event on the HTMLMediaElement,
which shows the controls. The controls then remain visible as long as
the media element itself or any part of the control retains focus, or
until the hide timer fires (which it will on a pause-play "cycle" for
instance).

BUG=135661

Review URL: https://codereview.chromium.org/297783004

git-svn-id: svn://svn.chromium.org/blink/trunk@174794 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rudimentary keyboard navigation support for <video>/<audio>

Remove the override of hasCustomFocusLogic() for HTMLMediaElement. This
allows focus navigation (<tab>ing) to reach the controls.

BUG=135661

Review URL: https://codereview.chromium.org/292173006

git-svn-id: svn://svn.chromium.org/blink/trunk@174795 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Adjust end position of a paragraph to clone during indent command

This patch adjusts end position of paragraph to clone during indent command to
satisfy cloneParagraphUnderNewElement assumption.

In the test case, we call  moveParagraphWithClones with |start| is text node,
and |end| is HEAD element, since HEAD element is visible by style.

BUG=351281
TEST=LayoutTests/editing/execCommand/indent-head-crash.html

Review URL: https://codereview.chromium.org/297263004

git-svn-id: svn://svn.chromium.org/blink/trunk@174796 bbb929c8-8fbe-4397-9dbb-9b2b20218538