Rename PageLifecycleObserver to PageVisibilityObserver

Rename PageLifecycleObserver to PageVisibilityObserver

Now that PageLifecycleObserver has only pageVisibilityChanged(),
it would make more sense to rename the class accordingly.

BUG=610176
Committed: https://crrev.com/13f83b3c919141de77bc6779cb793d37446b0ebe
Cr-Commit-Position: refs/heads/master@{#404623}

[haraken, 2016-07-11 07:40:35]

haraken@chromium.org changed reviewers:
+ dcheng@chromium.org

[haraken, 2016-07-11 07:40:35]

PTAL

[dcheng, 2016-07-11 07:45:09]

lgtm

[haraken, 2016-07-11 07:57:10]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2016-07-11 07:57:25]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-11 09:29:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-11 09:29:28]

CQ bit was unchecked.

[commit-bot: I haz the power, 2016-07-11 09:30:48]

Description was changed from

==========
Rename PageLifecycleObserver to PageVisibilityObserver

Now that PageLifecycleObserver has only pageVisibilityChanged(),
it would make more sense to rename the class accordingly.

BUG=610176
==========

to

==========
Rename PageLifecycleObserver to PageVisibilityObserver

Now that PageLifecycleObserver has only pageVisibilityChanged(),
it would make more sense to rename the class accordingly.

BUG=610176

Committed: https://crrev.com/13f83b3c919141de77bc6779cb793d37446b0ebe
Cr-Commit-Position: refs/heads/master@{#404623}
==========

[commit-bot: I haz the power, 2016-07-11 09:30:50]

Patchset 1 (id:??) landed as
https://crrev.com/13f83b3c919141de77bc6779cb793d37446b0ebe
Cr-Commit-Position: refs/heads/master@{#404623}