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Until this CL, TestingProfile had 3 distinct URLRequestContexts it would return to the user: one via profile->GetDefaultStoragePartition()->GetRequestContext(), one via profile->GetRequestContext(), and one via profile->GetResourceContext->GetRequestContext().  All of these had different cookie stores.  This CL unified them so they all return the one from profile->GetDefaultStoragePartition()->GetRequestContext(). This correctly mimics how production code works.

Doing this had a bunch of implications:
 (1) Removes TestingProfile::CreateRequestContext()/ResetRequestContext()
 (2) Changes MockRequestContext to share the URLRequestContext with TestingProfile.
 (3) TestingProfile now requires all BrowserThreads.

Point (3) effectively adds TestBrowserThreadBundle into a bunch more spots. Because of that, we also have the following changes:
  (a) AshTestBase now has a TestBrowserThreadBundle
  (b) Removed a bunch of real threads from tests.
  (c) TemplateUrlService has reworked synchronization semantics.
  (d) Removed MultiThreadTestHelper.
  (e) Added TestingIOThread class + testing API in IOThread to mock out various IO thread tasks which enervated with the new TestBrowserThreadBundle.

TBR=bauerb,brettw,isherman,joth,jyasskin,mattm,mmenke,mnissler,pkasting,rkc,rlp,satorux,tim,xians,joth
BUG=159193

Review URL: https://chromiumcodereview.appspot.com/17127002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@213272 0039d316-1c4b-4281-b951-d872f2087c98