Reland #3: Ensure WebView notifies desktop automation on creation,

Reland #3: Ensure WebView notifies desktop automation on creation, destruction, and change

Original issue: https://codereview.chromium.org/880063002
Previous reland attempt: https://codereview.chromium.org/895623003/
previous reland attempt 2: https://codereview.chromium.org/890013006/
- able to reproduce the flakes locally by running multiple copies of the same test in parallel.
- tracked the issues down to the following points/solutions:
1. in automation_node.js, we now fire a loadComplete event if we detect a loaded root within enableFrame's callback. Previously, there could be a situation where a tree was already finished loading so it never actually fires that load complete.
2. in automation_node.js, we now store the callback that fires childrenChanged and the loadComplete above before requesting the browser initiate tree only accessibility which sends down the data.
3. in chromevox_next_e2e_test_base.js, we now check that the url contains 'test' to avoid processing loadCompletes from other rootWebAreas (e.g. about:blank).

TBR=dmazzoni@chromium.org

Committed: https://crrev.com/4da650e88c859e6d1c2d82993cd6ed3376e77f80
Cr-Commit-Position: refs/heads/master@{#315785}

[David Tseng, 2015-02-10 00:03:12]

dtseng@chromium.org changed reviewers:
+ dmazzoni@chromium.org

[David Tseng, 2015-02-11 17:12:09]

The CQ bit was checked by dtseng@chromium.org

[commit-bot: I haz the power, 2015-02-11 17:12:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/907973004/20001

[commit-bot: I haz the power, 2015-02-11 17:18:55]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-11 17:19:51]

Patchset 2 (id:??) landed as
https://crrev.com/4da650e88c859e6d1c2d82993cd6ed3376e77f80
Cr-Commit-Position: refs/heads/master@{#315785}

[David Tseng, 2015-02-11 18:05:34]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/891633004/ by dtseng@chromium.org.

The reason for reverting is: Still flakes....