It's not just [] that return the element type of a List. Make the container optimization work for s…

sdk/lib/_internal/compiler/implementation/inferrer/simple_types_inferrer.dart

Index: sdk/lib/_internal/compiler/implementation/inferrer/simple_types_inferrer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/inferrer/simple_types_inferrer.dart	(revision 27800)
+++ sdk/lib/_internal/compiler/implementation/inferrer/simple_types_inferrer.dart	(working copy)
@@ -120,10 +120,6 @@
   }
 
   TypeMask refineReceiver(Selector selector, TypeMask receiverType) {
-    // If the receiver is based on an element, we let the type
-    // inferrer handle it. Otherwise, we might prevent it from finding
-    // one-level cycles in the inference graph.
-    if (receiverType.isElement) return receiverType;
     TypeMask newType = compiler.world.allFunctions.receiverType(selector);
     return receiverType.intersection(newType, compiler);
   }