Stop unfreezing tabs "frozen" for lazy loads

Stop unfreezing tabs "frozen" for lazy loads

When opening a tab in the background on Svelte devices, tabs are
marked as "frozen" without actually being frozen (no saved state).

* Make CompositorViewHolder load these tabs properly instead of
  trying to unfreeze them.

* Make Tab#unfreezeContents() protected so that nothing can handle
  this.

* Clear out pointers when destroying the objects and clean up
  destruction, in general.

* Stop destroying some TabObservers twice.

* Add a test to catch this.

* Moves process killing to the end of destroy() instead of the middle.

BUG=495877
Committed: https://crrev.com/f2c7f2a4c2332d104467eaf71651cfb6b3a18a13
Cr-Commit-Position: refs/heads/master@{#348755}

[gone, 2015-09-14 21:56:22]

dfalcantara@chromium.org changed reviewers:
+ dtrainor@chromium.org, mariakhomenko@chromium.org

[Maria, 2015-09-14 23:02:41]

lgtm

[gone, 2015-09-14 23:03:00]

The CQ bit was checked by dfalcantara@chromium.org

[commit-bot: I haz the power, 2015-09-14 23:04:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1337113007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1337113007/1

[commit-bot: I haz the power, 2015-09-14 23:12:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-14 23:13:35]

Patchset 1 (id:??) landed as
https://crrev.com/f2c7f2a4c2332d104467eaf71651cfb6b3a18a13
Cr-Commit-Position: refs/heads/master@{#348755}

[commit-bot: I haz the power, 2015-09-23 12:38:38]

Patchset 1 (id:??) landed as
https://crrev.com/f2c7f2a4c2332d104467eaf71651cfb6b3a18a13
Cr-Commit-Position: refs/heads/master@{#348755}