Consolidate TestURLFetcherFactory::SetFakeResponse

Remove the std::string version of the function and convert all callers
to the GURL version.

BUG=None
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/23625015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225952 0039d316-1c4b-4281-b951-d872f2087c98
Nudging sizes expectations after some gradual increases.

See bug for discussion.

TBR=sullivan@chromium.org
BUG=301526

Review URL: https://codereview.chromium.org/25058008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225953 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225953