Implement is-checks against type variables.

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

Index: sdk/lib/_internal/compiler/implementation/world.dart
diff --git a/sdk/lib/_internal/compiler/implementation/world.dart b/sdk/lib/_internal/compiler/implementation/world.dart
index 271629bf64132666df45a3b3aba08074886ca86e..0f94a5d6a03d8ff26b81d882a8fa00e09be514a0 100644
--- a/sdk/lib/_internal/compiler/implementation/world.dart
+++ b/sdk/lib/_internal/compiler/implementation/world.dart
@@ -60,7 +60,6 @@ class World {
     // (3) subclasses of (2) and (3).
 
     void potentiallyAddForRti(ClassElement cls) {
-      if (cls.typeVariables.isEmpty) return;
       if (classesNeedingRti.contains(cls)) return;
       classesNeedingRti.add(cls);
 
@@ -85,6 +84,10 @@ class World {
         if (!itf.isRaw) {
           potentiallyAddForRti(itf.element);
         }
+      } else if (type is TypeVariableType) {
+        TypeVariableElement variable = type.element;
+        ClassElement enclosing = variable.enclosingElement;

[ngeoffray, 2013/02/22 11:04:30]

Why this change?

+        potentiallyAddForRti(enclosing);
       }
     });
   }
@@ -112,7 +115,9 @@ class World {
   }
 
   bool needsRti(ClassElement cls) {
-    return classesNeedingRti.contains(cls) || compiler.enabledRuntimeType;
+    return classesNeedingRti.contains(cls) ||
+           compiler.enabledRuntimeType ||
+           compiler.hasVariableTypecheck;

[ngeoffray, 2013/02/22 11:04:30]

So any class needs rti when the check is on? Shouldn't we track the classes used
in a type variable, and the class that declares the type variable does a type
variable is check?

   }
 
   bool hasAnyUserDefinedGetter(Selector selector) {