Change DataReductionProxy browser_tests to use dataReductionProxy API.

Change DataReductionProxy browser_tests to use dataReductionProxy API.

The extension was changed to use preferences API rather than direct
settings API. This cl updates the test to use the same API.

Committed: https://crrev.com/9990fe47e3d3db3b245d480e17f37e615ded1040
Cr-Commit-Position: refs/heads/master@{#321840}

[Not at Google. Contact bengr, 2015-03-23 18:19:05]

kundaji@chromium.org changed reviewers:
+ bengr@chromium.org

[bengr, 2015-03-23 18:51:56]

lgtm

[Not at Google. Contact bengr, 2015-03-23 18:53:18]

The CQ bit was checked by kundaji@chromium.org

[commit-bot: I haz the power, 2015-03-23 18:53:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1026123002/1

[commit-bot: I haz the power, 2015-03-23 20:49:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-23 20:50:25]

Patchset 1 (id:??) landed as
https://crrev.com/9990fe47e3d3db3b245d480e17f37e615ded1040
Cr-Commit-Position: refs/heads/master@{#321840}