Revert "Implement interface types."

lib/compiler/implementation/ssa/codegen.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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   SsaCodeGeneratorTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA code generator';
 
 
   String generateMethod(WorkItem work, HGraph graph) {
@@ skipping 1447 matching lines @@
     beginExpression(JSPrecedence.LOGICAL_OR_PRECEDENCE);
     checkArray(input, '===');
     buffer.add(' || ');
     checkType(input, element);
     buffer.add(')');
     endExpression(JSPrecedence.LOGICAL_OR_PRECEDENCE);
     endExpression(JSPrecedence.LOGICAL_AND_PRECEDENCE);
   }
 
   void visitIs(HIs node) {
-    Type type = node.typeName;
-    Element element = type.element;
+    Element element = node.typeExpression;
     if (element.kind === ElementKind.TYPE_VARIABLE) {
       compiler.unimplemented("visitIs for type variables");
-    } else if (element.kind === ElementKind.TYPEDEF) {
-      compiler.unimplemented("visitIs for typedefs");
     }
     compiler.registerIsCheck(element);
     LibraryElement coreLibrary = compiler.coreLibrary;
-    ClassElement objectClass = compiler.objectClass;
+    ClassElement objectClass = coreLibrary.find(const SourceString('Object'));
     HInstruction input = node.expression;
     if (node.nullOk) {
       beginExpression(JSPrecedence.LOGICAL_OR_PRECEDENCE);
       checkNull(input);
       buffer.add(' || ');
     }
 
     if (element === objectClass || element === compiler.dynamicClass) {
       // The constant folder also does this optimization, but we make
       // it safe by assuming it may have not run.
@@ skipping 397 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endElse(HIf node) {
     if (node.elseBlock.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }