Analyzer: Avoid self reference test if Uri given
Analyzer: Avoid self reference test if Uri given

This trims the overhead of `PackageUriResolver.resolveAbsolute` from 12%
to 5% of stand-alone analysis of one 3000 package app.

R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org/1817423002 .

dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk