Adjusts dart2js SSA builder to tolerate method type arguments.

pkg/compiler/lib/src/js_backend/runtime_types.dart

Index: pkg/compiler/lib/src/js_backend/runtime_types.dart
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types.dart b/pkg/compiler/lib/src/js_backend/runtime_types.dart
index 036e52ae628f032a01fea020174d2e857ceed1a2..eec53cb2c457698d7965fb8dc1f965bcc5eb501f 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -252,7 +252,12 @@ class _RuntimeTypes implements RuntimeTypes {
     compiler.resolverWorld.isChecks.forEach((DartType type) {
       if (type.isTypeVariable) {
         TypeVariableElement variable = type.element;
-        classesUsingTypeVariableTests.add(variable.typeDeclaration);
+        // TODO(eernst): When generic method support is complete enough to
+        // include a runtime value for method type variables, this may need to
+        // be updated.
+        if (variable.typeDeclaration is ClassElement) {
+          classesUsingTypeVariableTests.add(variable.typeDeclaration);
+        }
       }
     });
     // Add is-checks that result from classes using type variables in checks.