Implement is-checks against type variables.

sdk/lib/_internal/compiler/implementation/resolution/members.dart

Index: sdk/lib/_internal/compiler/implementation/resolution/members.dart
diff --git a/sdk/lib/_internal/compiler/implementation/resolution/members.dart b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
index 52da7811bd4f35540899698e11dbc7dbdf1c00ab..ea09e938038a18e676ba551af6907b3fb1e6148c 100644
--- a/sdk/lib/_internal/compiler/implementation/resolution/members.dart
+++ b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
@@ -2478,10 +2478,11 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
         itf.typeArguments.forEach((DartType argument) {
           analyzeTypeArgument(type, argument);
         });
+      } else if (type is TypeVariableType) {
+        compiler.world.registerTypeVariableCheck(currentClass);
+        compiler.backend.registerRuntimeType();
       }
-      // TODO(ngeoffray): Also handle cases like:
-      // 1) a is T
-      // 2) T a (in checked mode).
+      // TODO(ngeoffray): Also handle T a (in checked mode).
     }
     return type;
   }