Use TestingProfile::Builder::AddTestingFactory at ChromeRenderViewHostTestHarness

This test harness is overriding the SigninManagerFactory for its TestingProfiles too late, after the Profile has already been created. Any services that depend on the SigninManager and get created with the Profile are thus left with a dead pointer (e.g. UserPolicySigninService).

This change sets the fake factory before the TestingProfile gets created. It also makes ChromeRenderViewHostTestHarness more consistent by using the fake factory for every TestingProfile created, not just the first one.

BUG=345617

Review URL: https://codereview.chromium.org/189443008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256379 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256379