Allow load if play() is immediately called when preload == 'none'

Allow load if play() is immediately called when preload == 'none'

This fixes a bug where the load gets blocked by preload == 'none'
eventhough JavaScript has called play() after setting the src
attribute. This particular bug only appears if play() is called before
the JavaScript code relinquishes control back to the UA.

Tests cases were added to make sure that immediate load() and play()
calls both trigger loading. Before this change, only immediate load()
calls ignored the preload == "none" state.

BUG=177870
TEST=LayoutTest/media/video-preload.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175590

[adamk, 2014-06-05 17:23:49]

lgtm

[acolwell GONE FROM CHROMIUM, 2014-06-05 17:34:42]

The CQ bit was checked by acolwell@chromium.org

[commit-bot: I haz the power, 2014-06-05 17:35:07]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/acolwell@chromium.org/313173008/20001

[commit-bot: I haz the power, 2014-06-05 18:11:19]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/7057)

[commit-bot: I haz the power, 2014-06-05 18:14:30]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-06-05 18:14:31]

Try jobs failed on following builders:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/7058)

[acolwell GONE FROM CHROMIUM, 2014-06-05 18:30:57]

The CQ bit was checked by acolwell@chromium.org

[commit-bot: I haz the power, 2014-06-05 18:32:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/acolwell@chromium.org/313173008/40001

[commit-bot: I haz the power, 2014-06-05 20:08:52]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/7059)

[commit-bot: I haz the power, 2014-06-05 20:11:35]

Change committed as 175590