If the element or selector is a setter, make sure to use the runtime setter name to know whether we…

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(revision 27800)
+++ sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(working copy)
@@ -1577,6 +1577,9 @@
   /// Called when [:const Symbol(name):] is seen.
   void registerConstSymbol(String name, TreeElements elements) {
     symbolsUsed.add(name);
+    if (name.endsWith('=')) {
+      symbolsUsed.add(name.substring(0, name.length - 1));
+    }
   }
 
   /// Called when [:new Symbol(...):] is seen.