google_apis: Add GetURL() to test_server::HttpServer

Add GetURL() and remove the return value from Register* functions,
as using GetURL() at the call sites of URLFetcher makes the code
clearer about target URLs.

Along the way, add tests for GetBaseURL(), GetURL(),
RegisterDefaultResponse(), RegisterFileResponse(), as well as
concurrent fetches.

BUG=148710
TEST=none; just changing test utils.

Review URL: https://codereview.chromium.org/11416030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168482 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed