- Move length getter and setter interceptors to the new interceptor scheme.

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 15149)
+++ sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(working copy)
@@ -655,6 +655,8 @@
   ClassElement jsNullClass;
   ClassElement jsBoolClass;
   ClassElement objectInterceptorClass;
+  Element jsArrayLength;
+  Element jsStringLength;
   Element getInterceptorMethod;
   bool _interceptorsAreInitialized = false;
 
@@ -768,6 +770,10 @@
         compiler.findInterceptor(const SourceString('JSFunction'));
     jsBoolClass =
         compiler.findInterceptor(const SourceString('JSBool'));
+    jsArrayLength =
+        jsArrayClass.lookupLocalMember(const SourceString('length'));
+    jsStringLength =
+        jsStringClass.lookupLocalMember(const SourceString('length'));
   }
 
   void addInterceptors(ClassElement cls) {