dart2js cps: Handle error cases.

pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
index d511047e94cea2655050a253f9616fc0f995083e..df9e84e53c0bb226f89748a989ed6be57c7caaf4 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
@@ -2485,6 +2485,7 @@ class JsIrBuilder extends IrBuilder {
 
   ir.Primitive buildThis() {
     if (jsState.receiver != null) return jsState.receiver;
+    assert(state.thisParameter != null);
     return state.thisParameter;
   }
 
@@ -2587,6 +2588,11 @@ class JsIrBuilder extends IrBuilder {
       return addPrimitive(new ir.ReadTypeVariable(variable, target));
     }
   }
+
+  ir.Primitive buildInvocationMirror(Selector selector,
+                                     List<ir.Primitive> arguments) {
+    return addPrimitive(new ir.CreateInvocationMirror(selector, arguments));
+  }
 }