Eagerly infer the element type of const lists in the simple inferrer.

sdk/lib/_internal/compiler/implementation/types/container_tracer.dart

Index: sdk/lib/_internal/compiler/implementation/types/container_tracer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/types/container_tracer.dart	(revision 24128)
+++ sdk/lib/_internal/compiler/implementation/types/container_tracer.dart	(working copy)
@@ -95,6 +95,8 @@
       var internal = inferrer.internal;
       // Walk over all created [ContainerTypeMask].
       internal.concreteTypes.values.forEach((ContainerTypeMask mask) {
+        // The element type has already been set for const containers.
+        if (mask.elementType != null) return;
         mask.elementType = new TracerForConcreteContainer(
             mask, this, compiler, inferrer).run();
       });