Fix subpixel font scaling for DirectWrite

Implement support for subpixel font scaling for the Windows DirectWrite
backend and change how the subpixel flag is set to use the SkPaint::
kSubpixelText_Flag flag instead of the method as otherwise the setFlags
call clears the subpixel flag.

BUG=25541
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/239283010

git-svn-id: svn://svn.chromium.org/blink/trunk@171817 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix compositing chicken-egg bug.

nodeImage and dragImageForSelection set the base background
color to transparent, which requires the compositing state
to be up to date. Turns out that they don't need to
set the base background color at all.

http://trac.webkit.org/changeset/144841 changed the color
from white to transparent, but it turns out that just not
setting the base background color at all works the same.
At least, in the test case in that patch it does.

The author of the original line that set the color to
white doesn't remember why it was needed:
https://bugs.webkit.org/show_bug.cgi?id=110512#c1

BUG=362750

Review URL: https://codereview.chromium.org/240543003

git-svn-id: svn://svn.chromium.org/blink/trunk@171818 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix destruction order of Media element and MediaKeys.

When a MediaKeys object is associated with a Media element, during destruction
of the Media element, we want to destroy the media player before destroying the
CDM. This is because we assume the CDM will outlive the media pipeline.

Note that this doesn't resolve the more general issue that setMediaKeys(0) can
be called when the media pipeline is still using the CDM. That issue is tracked
by http://crbug.com/330324.

BUG=360345
TEST=Added a new layout test to cover the issue.

Review URL: https://codereview.chromium.org/238123002

git-svn-id: svn://svn.chromium.org/blink/trunk@171819 bbb929c8-8fbe-4397-9dbb-9b2b20218538
rAc: remove deprecated checkValidityWithoutDispatchingEvents() now that it's not used.

R=tkent@chromium.org
BUG=361843

Review URL: https://codereview.chromium.org/233483003

git-svn-id: svn://svn.chromium.org/blink/trunk@171821 bbb929c8-8fbe-4397-9dbb-9b2b20218538