Clean up app list webstore_provider_browsertest.

Clean up app list webstore_provider_browsertest.

Record whether a query is pending and use it to decide when to wait
(previously, it would wait if ANY previous query was ever pending, which
"just happened" to work for the specific test cases).

Changed some ASSERT into EXPECT.

Use more descriptive special strings for HTTP errors, rather than the
exact same string as the query, which is confusing.

Document the test cases properly.

Reformat the source according to ClangFormat.

BUG=481837
Committed: https://crrev.com/a44e9ca99fb9450a40d015723d23625fd3dff218
Cr-Commit-Position: refs/heads/master@{#329327}

[Matt Giuca, 2015-05-08 04:55:28]

mgiuca@chromium.org changed reviewers:
+ calamity@chromium.org

[Matt Giuca, 2015-05-08 04:55:29]

This is a precursor to https://codereview.chromium.org/1110903002. There was so
much stuff to fix in this test (including a big formatting required) that I
decided to do it separately so it will be easier to read the changes I am making
to the test in the next CL.

[calamity, 2015-05-11 06:00:21]

Reformat the CL description to have bullet points and make all points have the
same tense.

[calamity, 2015-05-11 06:28:37]

lgtm

[Matt Giuca, 2015-05-12 01:29:06]

The CQ bit was checked by mgiuca@chromium.org

[commit-bot: I haz the power, 2015-05-12 01:30:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1133543003/1

[commit-bot: I haz the power, 2015-05-12 02:24:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-12 02:25:47]

Patchset 1 (id:??) landed as
https://crrev.com/a44e9ca99fb9450a40d015723d23625fd3dff218
Cr-Commit-Position: refs/heads/master@{#329327}