dart2js: support tear-offs in the startup emitter.

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

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index ba39217b20b4e12b51c115c0fd428ac810a4323f..91c47651a21927488a844996a1d09347214b68ba 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -242,10 +242,10 @@ class JavaScriptBackend extends Backend {
   static const String START_ROOT_ISOLATE = 'startRootIsolate';
 
 
+  String get patchVersion => emitter.patchVersion;
+  
   bool get supportsReflection => emitter.emitter.supportsReflection;
 
-  String get patchVersion => USE_LAZY_EMITTER ? 'lazy' : 'full';
-
   final Annotations annotations;
 
   /// Reference to the internal library to lookup functions to always inline.