Fix sub-pixel handling of transparency layers

Transparency layers were implemented before composited layers
were made to be fully sub-pixel aware. Blink r164561 was the
sub-pixel fix for composited layers, which caused them to behave
differently than transparency layers leading to off-by-one
errors. This patch teaches transparency layers about sub-pixel.

BUG=347521

Review URL: https://codereview.chromium.org/180163008

git-svn-id: svn://svn.chromium.org/blink/trunk@168450 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Extract CSPDirectiveList from ContentSecurityPolicy.

BUG=346642

Review URL: https://codereview.chromium.org/180273012

git-svn-id: svn://svn.chromium.org/blink/trunk@168451 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove MediaControls::showVolumeSlider()

This is a remnant from WebKit when there was a volume slider container
that could be shown and hidden. What remains is essentially dead code,
because at most it shows the slider when m_mediaController->hasAudio(),
but MediaControls::reset() already does that.

BUG=341813

Review URL: https://codereview.chromium.org/176883020

git-svn-id: svn://svn.chromium.org/blink/trunk@168452 bbb929c8-8fbe-4397-9dbb-9b2b20218538