Reuse relative URI resolution logic.
Reuse relative URI resolution logic.

Change-Id: Ic27b0870bde9842bf9bd60498b5410e7beb570af
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/220224
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Reviewed-by: Keerti Parthasarathy <50d1d8bfaf73a210aebf5aef847d5b7b93955336@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