Fix network quality estimator tests

Fix network quality estimator tests

(1) Enabling the tests that were disabled on Windows:
Windows requires nested classes to have EXPORT macros.

(2) Enabling the flaky test:
Sometimes the RTT observation may be equal to
base::TimeDelta() because of low timer granularity.
This was causing one of the network quality estimator test to flake.

BUG=504058, 492410
Committed: https://crrev.com/5659c35e1ee2d27bc4780a3908607645334fbb84
Cr-Commit-Position: refs/heads/master@{#336175}

[tbansal1, 2015-06-25 01:36:13]

[email protected] changed reviewers:
+ [email protected]

[tbansal1, 2015-06-25 01:36:14]

ptal. thanks a lot for your time!!

[tbansal1, 2015-06-25 01:36:38]

ptal. thanks a lot for your time!!

[pauljensen, 2015-06-25 03:11:21]

lgtm

[tbansal1, 2015-06-25 15:20:08]

The CQ bit was checked by [email protected]

[tbansal1, 2015-06-25 15:20:08]

The patchset sent to the CQ was uploaded after l-g-t-m from
[email protected]
Link to the patchset: https://codereview.chromium.org/1210743002/#ps20001
(title: "rebased")

[commit-bot: I haz the power, 2015-06-25 15:20:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1210743002/20001

[commit-bot: I haz the power, 2015-06-25 16:49:45]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-25 16:50:37]

Patchset 2 (id:??) landed as
https://crrev.com/5659c35e1ee2d27bc4780a3908607645334fbb84
Cr-Commit-Position: refs/heads/master@{#336175}