Do not fire an initial periodic timeupdate event while currentTime is 0

Do not fire an initial periodic timeupdate event while currentTime is 0

m_lastTimeUpdateEventMovieTime has been initialized to infinity for as
long as the code has existed: http://trac.webkit.org/changeset/41907

This may be the cause of a spurious timeupdate event on Mac 10.9 in a
recently added test: https://codereview.chromium.org/578243003

TEST=media/gc-while-playing.html

BUG=400659
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=182442

[philipj_slow, 2014-09-22 13:36:28]

philipj@opera.com changed reviewers:
+ fs@opera.com, scherkus@chromium.org

[philipj_slow, 2014-09-22 13:36:29]

PTAL. Instead of https://codereview.chromium.org/574883002

[fs, 2014-09-22 13:54:03]

Seems reasonable to me, so LGTM. Scherkus probably has a fresh recollection of
this area though, so his "opinion" may be of interest as well.

[philipj_slow, 2014-09-22 14:25:31]

Yep, awaiting scherkus' feedback before landing.

[scherkus (not reviewing), 2014-09-22 17:51:57]

lgtm

[scherkus (not reviewing), 2014-09-22 17:53:14]

The CQ bit was checked by scherkus@chromium.org

[commit-bot: I haz the power, 2014-09-22 17:53:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/587373002/1

[commit-bot: I haz the power, 2014-09-22 18:45:46]

Committed patchset #1 (id:1) as 182442