Remove deprecated class WebContentsObserverAndroid and cleanup existing usages.

Remove deprecated class WebContentsObserverAndroid and cleanup existing usages.

In continuation of the CL https://codereview.chromium.org/589113002/
this CL removes deprecated class WebContentsObserverAndroid and
cleans up existing usage of this class where ever it is occured.

This patch will be landed when external repositories has renamed
WebContentsObserverAndroid to WebContentsObserver

BUG=396118
Committed: https://crrev.com/1365c44bfc346304ccd36db4aac058b439420b70
Cr-Commit-Position: refs/heads/master@{#300426}

[wajahat, 2014-10-20 12:39:00]

wajahat.s@samsung.com changed reviewers:
+ nyquist@chromium.org, yfriedman@chromium.org

[wajahat, 2014-10-20 12:39:01]

PTAL, Thanks!

[Yaron, 2014-10-20 18:11:55]

lgtm

[nyquist, 2014-10-20 22:24:05]

lgtm

[nyquist, 2014-10-20 22:25:26]

The external dependencies of this CL has landed.

[wajahat, 2014-10-21 05:32:14]

The CQ bit was checked by wajahat.s@samsung.com

[commit-bot: I haz the power, 2014-10-21 05:33:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/650333003/1

[commit-bot: I haz the power, 2014-10-21 06:15:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-21 06:16:24]

Patchset 1 (id:??) landed as
https://crrev.com/1365c44bfc346304ccd36db4aac058b439420b70
Cr-Commit-Position: refs/heads/master@{#300426}