dart2js: Fix check for support of reflection.

pkg/compiler/lib/src/js_emitter/code_emitter_task.dart

Index: pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
diff --git a/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart b/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
index d4530ad392d289b3c70a039a4416425046ec21f4..cdcc609c5384937fd5e7f1245222b0f0b4c33df6 100644
--- a/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
+++ b/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
@@ -152,6 +152,9 @@ abstract class Emitter {
   /// the program, and returns the size of the generated output.
   int emitProgram(ProgramBuilder programBuilder);
 
+  /// Returns true, if the emitter supports reflection.
+  bool get supportsReflection;
+
   /// Returns the JS function that must be invoked to get the value of the
   /// lazily initialized static.
   jsAst.Expression isolateLazyInitializerAccess(FieldElement element);