Implement is-checks against type variables.

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

Index: sdk/lib/_internal/compiler/implementation/dart_types.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart_types.dart b/sdk/lib/_internal/compiler/implementation/dart_types.dart
index b9bdbd73d903a7da25e4aeba8708a7654d02ec14..c79571b1a23723c948510527c839eeb8e7e82d00 100644
--- a/sdk/lib/_internal/compiler/implementation/dart_types.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart_types.dart
@@ -75,6 +75,7 @@ abstract class DartType {
    */
   bool get isMalformed => false;
 
+  bool get containsTypeVariable => false;
   /**
    * Calls [f] with each [MalformedType] within this type.
    *
@@ -126,6 +127,8 @@ class TypeVariableType extends DartType {
 
   SourceString get name => element.name;
 
+  bool get containsTypeVariable => true;
+
   DartType subst(Link<DartType> arguments, Link<DartType> parameters) {
     if (parameters.isEmpty) {
       assert(arguments.isEmpty);
@@ -299,6 +302,15 @@ abstract class GenericType extends DartType {
 
   GenericType(Link<DartType> this.typeArguments, bool this.isMalformed);
 
+  bool get containsTypeVariable {
+    for (Link<DartType> arguments = typeArguments;
+	 !arguments.isEmpty;
+	 arguments = arguments.tail) {
+      if (arguments.head.containsTypeVariable) return true;
+    }
+    return false;
+  }
+
   TypeDeclarationElement get element;
 
   /// Creates a new instance of this type using the provided type arguments.