Make MockAnalysisDriver implement AnalysisDriver, not extend.
Make MockAnalysisDriver implement AnalysisDriver, not extend.

The way we used to configure it does not work with changed I want to
make, specifically we were given SourceFactory with no resolves,
so no DartUriResolver, so no SDK.

R=1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com

Change-Id: Ibf798aae1792366cfbe240f9781038568936146d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149384
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk