DOMException use String instead of char*

BUG=None

Review URL: https://chromiumcodereview.appspot.com/19684003

git-svn-id: svn://svn.chromium.org/blink/trunk@154523 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix HTMLMediaElement seek's timeupdate scheduling

Moves timeupdate event scheduling from seek to finishSeek to match spec.
Adds layout tests to verify spec's expected events and attributes while seeking to duration and middle of a video.

BUG=261279,261296
R=acolwell@chromium.org,adamk@chromium.org
TEST=media and http/tests/media layout tests pass locally on linux

Review URL: https://chromiumcodereview.appspot.com/19719002

git-svn-id: svn://svn.chromium.org/blink/trunk@154524 bbb929c8-8fbe-4397-9dbb-9b2b20218538