Simplify MessageChannel's IDL

Simplify MessageChannel's IDL by removing useless Constructor-related
extended attributes. Those have no effect since we use custom code for
the constructor.

R=haraken

Review URL: https://chromiumcodereview.appspot.com/23055004

git-svn-id: svn://svn.chromium.org/blink/trunk@156289 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add json responseType support to XMLHttpRequest

BUG=119256

Review URL: https://chromiumcodereview.appspot.com/21600002

git-svn-id: svn://svn.chromium.org/blink/trunk@156290 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Set DocumentTimeline's current time when setting its zero time

When CSS Animations are created, they are added to the DocumentTimeline, which
immediately updates their timing parameters. This occurs before
DocumentTimeline::serviceAnimations() is called, so the DocumentTimeline's
current time must be set as soon as the zero time is available.

BUG=240653
R=dstockwell

Review URL: https://chromiumcodereview.appspot.com/22882006

git-svn-id: svn://svn.chromium.org/blink/trunk@156291 bbb929c8-8fbe-4397-9dbb-9b2b20218538