Implement interface types.

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
diff --git a/lib/compiler/implementation/ssa/codegen.dart b/lib/compiler/implementation/ssa/codegen.dart
index 91f179dc4a9da9b9577922cbbe83d70de4e0b08f..90f33480dd0a8e97746adad9cb9677e351f97d6e 100644
--- a/lib/compiler/implementation/ssa/codegen.dart
+++ b/lib/compiler/implementation/ssa/codegen.dart
@@ -1446,13 +1446,16 @@ class SsaCodeGenerator implements HVisitor {
   }
 
   void visitIs(HIs node) {
-    Element element = node.typeExpression;
+    Type type = node.typeName;

[ahe, 2012/04/12 15:05:23]

I don't see how typeName is an improvement over typeExpression. I'd expect the
type of something called fooName to be a String, Identifier, or SourceString.

+    Element element = type.element;
     if (element.kind === ElementKind.TYPE_VARIABLE) {
       compiler.unimplemented("visitIs for type variables");

[ahe, 2012/04/12 15:05:23]

Please add this argument: "instruction: node"

+    } else if (element.kind === ElementKind.TYPEDEF) {
+      compiler.unimplemented("visitIs for typedefs");

[ahe, 2012/04/12 15:05:23]

Ditto.

     }
     compiler.registerIsCheck(element);
     LibraryElement coreLibrary = compiler.coreLibrary;
-    ClassElement objectClass = coreLibrary.find(const SourceString('Object'));
+    ClassElement objectClass = compiler.objectClass;
     HInstruction input = node.expression;
     if (node.nullOk) {
       beginExpression(JSPrecedence.LOGICAL_OR_PRECEDENCE);