Revert r22847: some dart2dart tests fail.

sdk/lib/_internal/compiler/implementation/compiler.dart

 // Copyright (c) 2012, 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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 1006 matching lines @@
   FunctionType computeFunctionType(Element element,
                                    FunctionSignature signature) {
     return withCurrentElement(element,
         () => resolver.computeFunctionType(element, signature));
   }
 
   reportWarning(Node node, var message) {
     if (message is TypeWarning) {
       // TODO(ahe): Don't supress these warning when the type checker
       // is more complete.
+      if (identical(message.message.kind, MessageKind.NOT_ASSIGNABLE)) return;
       if (identical(message.message.kind, MessageKind.MISSING_RETURN)) return;
       if (identical(message.message.kind, MessageKind.MAYBE_MISSING_RETURN)) {
         return;
       }
     }
     SourceSpan span = spanFromNode(node);
 
     reportDiagnostic(span, 'Warning: $message', api.Diagnostic.WARNING);
   }
 
@@ skipping 287 matching lines @@
 
   void close() {}
 
   toString() => name;
 
   /// Convenience method for getting an [api.CompilerOutputProvider].
   static NullSink outputProvider(String name, String extension) {
     return new NullSink('$name.$extension');
   }
 }