Fix bug in inferrer for the computation of callers: we need to keep track of what is the called nod…

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 27195)
+++ sdk/lib/_internal/compiler/implementation/types/container_tracer.dart	(working copy)
@@ -264,6 +264,9 @@
     // [potentialType] can be null if we did not find any instruction
     // that adds elements to the list.
     if (potentialType == null) {
+      if (_VERBOSE) {
+        print('Found empty type for $analyzedNode $startElement');
+      }
       mask.elementType = new TypeMask.nonNullEmpty();
       return;
     }