Visit all unit declarations in their declared order in ResolverVisitor.
Visit all unit declarations in their declared order in ResolverVisitor.

The case which required visiting non-class declarations first is
implemented now in a better way. So, we don't need the old workaround.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org/1903793002 .

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