Canonicalize mixin applications by their name

pkg/front_end/lib/src/fasta/compile_platform.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.compile_platform;
 
 import 'dart:async' show
     Future;
 
 import 'package:kernel/verifier.dart' show
@@ skipping 10 matching lines @@
 
 import 'compiler_context.dart' show
     CompilerContext;
 
 import 'errors.dart' show
     InputError;
 
 import 'kernel/kernel_target.dart' show
     KernelTarget;
 
-import 'package:kernel/ast.dart' show
-    Program;
-
 import 'dill/dill_target.dart' show
     DillTarget;
 
 import 'translate_uri.dart' show
     TranslateUri;
 
 import 'ast_kind.dart' show
     AstKind;
 
 Future main(List<String> arguments) async {
@@ skipping 41 matching lines @@
       ticker.logMs("Verified program");
     } catch (e, s) {
       exitCode = 1;
       print("Verification of program failed: $e");
       if (s != null && c.options.verbose) {
         print(s);
       }
     }
   }
 }