Support the DPR header for client hints.

As specified in
https://github.com/igrigorik/http-client-hints/blob/master/draft-grigorik-http-client-hints-01.txt#L255

Similar to a DPR specification in srcset, the DPR header should cause us
to divide the intrinsic height by the dpr.

BUG=303863
R=pdr@chromium.org
CC=yoav@yoav.ws

Review URL: https://codereview.chromium.org/46313002

git-svn-id: svn://svn.chromium.org/blink/trunk@160843 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Fix fonts inspection renderer crash

This patch fixes fonts inspection renderer crash. It happened due to
attempt to put "empty" key in the hashmap.

BUG=312398

Review URL: https://codereview.chromium.org/48633004

git-svn-id: svn://svn.chromium.org/blink/trunk@160844 bbb929c8-8fbe-4397-9dbb-9b2b20218538
start/stop method for AudioBufferSourceNodes and OscillatorNodes can take no args.

For AudioBufferSourceNodes, see
http://webaudio.github.io/web-audio-api/#methodsandparams-AudioBufferSourceNode

For OscillatorNodes, see https://github.com/WebAudio/web-audio-api/issues/249

BUG=305829,306141

Review URL: https://codereview.chromium.org/26913005

git-svn-id: svn://svn.chromium.org/blink/trunk@160845 bbb929c8-8fbe-4397-9dbb-9b2b20218538