* Use a std::map instead of std::vector for logarithmic search time.
 * Reduce the number of structs and make them private instead of
   protected since they arn't used outside of the base class.
 * Fix the SRV cache member name.

BUG=angle:520

Change-Id: I5158c1d46523f46158c51cd68044f7c915a3de03
Reviewed-on: https://chromium-review.googlesource.com/217335Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>