Add MediaSession runtime flag along with stub MediaSession object

Implementation of the MediaSession specification will happen behind
the runtime flag 'MediaSession'.

Add a virtual testsuite for running tests with MediaSession flag. This
way we don't have to have the flag enabled when running LayoutTests in
general, only when running MediaSession tests.

Intent to implement:

https://groups.google.com/a/chromium.org/d/msg/blink-dev/dLWDxYgxzQ8/vXt0ntWFNBwJ

BUG=497735

Review URL: https://codereview.chromium.org/1206283002

git-svn-id: svn://svn.chromium.org/blink/trunk@198049 bbb929c8-8fbe-4397-9dbb-9b2b20218538
12 files changed
tree: 264734f064b8b3a19494512321ab8747f641d8a8
  1. third_party/