Fix some warnings.

lib/compiler/implementation/dart_backend/backend.dart

Index: lib/compiler/implementation/dart_backend/backend.dart
diff --git a/lib/compiler/implementation/dart_backend/backend.dart b/lib/compiler/implementation/dart_backend/backend.dart
index c28f41669fb1b6a6459c321ba65ee648f22ee231..1100be50ac1c4508b0eabf235ba8b5ddd9742443 100644
--- a/lib/compiler/implementation/dart_backend/backend.dart
+++ b/lib/compiler/implementation/dart_backend/backend.dart
@@ -131,8 +131,9 @@ class DartBackend extends Backend {
     workQueue.addAll(
         classMembers.getKeys().map((classElement) => classElement.type));
     workQueue.addAll(compiler.resolverWorld.isChecks);
-    DartType typeErrorType =
-        compiler.coreLibrary.find(new SourceString('TypeError')).type;
+    Element typeErrorElement =
+        compiler.coreLibrary.find(new SourceString('TypeError'));
+    DartType typeErrorType = typeErrorElement.computeType(compiler);
     if (workQueue.indexOf(typeErrorType) != -1) {
       return false;
     }
@@ -347,8 +348,9 @@ class DartBackend extends Backend {
       constructor.type = new FunctionType(
           compiler.types.voidType, const EmptyLink<DartType>(),
           constructor);
+      ClassNode classNode = classElement.parseNode(compiler);

[ahe, 2012/10/03 14:56:33]

Couldn't you change the return type?

[karlklose, 2012/10/04 08:50:00]

Done.

       constructor.cachedNode = new FunctionExpression(
-          new Send(receiver: classElement.parseNode(compiler).name,
+          new Send(receiver: classNode.name,
                    selector: synthesizedIdentifier),
           new NodeList(beginToken: new StringToken(OPEN_PAREN_INFO, '(', -1),
                        endToken: new StringToken(CLOSE_PAREN_INFO, ')', -1),