[SocketStream unittest] Add GetSeenEvents check and method reordering for readability

Add GetSeenEvents checking to NullContextSocketStreamShouldNotCrash test.

Check if all expectation in data provider have been consumed.

SetOnStartOpenConnection is used to set handler for OnStartOpenConnection
delegate method which is invoked earlier than OnConnected. Set it before
calling SetOnConnected so that the order of expectation setting is the same
as actual event happening order.

BUG=

Review URL: https://codereview.chromium.org/26162003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228118 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228118
Reland "Add unit test for google_apis::RequestSender."

This CL was once committed as r227731 and reverted at r227738 since it broke
memory bots. This one fixes the issue.

BUG=161207, 251104
R=hashimoto@chromium.org

Review URL: https://codereview.chromium.org/26740004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228119 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228119