Update TestURLRequest constructor interface in extensions unit tests.

Update TestURLRequest constructor interface in extensions unit tests.

The TestURLRequest constructor interface is being expanded to allow separate
initialization arguments for the URLRequestContext and NetworkDelegate.
Most of the time this means making it explicit that the test in question
uses no network delegate.  This is motivated by a desire to remove external
accesses to a request context's delegate.  (If a block of code needs to
use a NetworkDelegate, it should not query the URLRequestContext for it,
but instead should already have access to whatever delegate the context uses.)

BUG=146587
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=187192

[tedv, 2013-02-25 03:15:01]

This issue depends on https://codereview.chromium.org/12328072/ which adds the
new constructor interface for TestURLRequest.

[Matt Perry, 2013-02-25 22:04:02]

lgtm

[commit-bot: I haz the power, 2013-03-10 02:33:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tedv@chromium.org/12328079/4001

[commit-bot: I haz the power, 2013-03-10 04:34:39]

Change committed as 187192