Don't report redundant type errors in strong mode.

pkg/analyzer/lib/src/task/strong/info.dart

 // Copyright (c) 2015, 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.
 
 /// Defines static information collected by the type checker and used later by
 /// emitters to generate code.
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.info;
 
@@ skipping 16 matching lines @@
   String get name => 'STRONG_MODE_ASSIGNMENT_CAST';
 
   toErrorCode() => new HintCode(name, message);
 }
 
 // Coercion which casts one type to another
 class Cast extends Coercion {
   Cast(DartType fromType, DartType toType) : super(fromType, toType);
 }
 
+
+// TODO(rnystrom): Analyzer no longer produces or uses anything except Cast,
+// so this should be eliminated once DDC no longer uses it.
 // The abstract type of coercions mapping one type to another.
 // This class also exposes static builder functions which
 // check for errors and reduce redundant coercions to the identity.
 abstract class Coercion {
   final DartType fromType;
   final DartType toType;
   Coercion(this.fromType, this.toType);
   static Coercion cast(DartType fromT, DartType toT) => new Cast(fromT, toT);
   static Coercion error() => new CoercionError();
   static Coercion identity(DartType type) => new Identity(type);
@@ skipping 519 matching lines @@
         super(expression);
 
   @override
   List<Object> get arguments => [node, baseType, expectedType];
   @override
   String get message => 'Type check failed: {0} ({1}) is not of type {2}';
 
   @override
   String get name => 'STRONG_MODE_STATIC_TYPE_ERROR';
 }