Don't change the media controls visibility in MediaControls::reset()

Don't change the media controls visibility in MediaControls::reset()

reset() is called from a number of places with the expectation of
putting the controls into the state they would be if created anew.

One such place is via HTMLMediaElement::preDispatchEventHandler, where
the controls are reset when entering or exiting fullscreen. This has a
very strange side-effect, namely that dispatching a synthetic
webkitfullscreenchange event on a video will cause the media controls to
become visible.

It would be rather messy to write a layout test for this, and it would
be slow to run, so instead add unit tests to test this more directly.

R=fs@opera.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201126

[philipj_slow, 2015-08-25 09:10:24]

The CQ bit was checked by philipj@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2015-08-25 09:10:37]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1319433003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1319433003/1

[fs, 2015-08-25 09:18:20]

lgtm

[commit-bot: I haz the power, 2015-08-25 10:22:59]

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

[commit-bot: I haz the power, 2015-08-25 10:23:00]

Dry run: This issue passed the CQ dry run.

[philipj_slow, 2015-08-25 11:23:39]

The CQ bit was checked by philipj@opera.com

[commit-bot: I haz the power, 2015-08-25 11:23:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1319433003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1319433003/1

[commit-bot: I haz the power, 2015-08-25 11:28:41]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201126