Do not apply optimizations based on an element if that element cannot be resolved.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/elements/elements.dart	(revision 16853)
+++ sdk/lib/_internal/compiler/implementation/elements/elements.dart	(working copy)
@@ -121,6 +121,8 @@
       const ElementKind('error', ElementCategory.NONE);
   static const ElementKind MALFORMED_TYPE =
     const ElementKind('malformed', ElementCategory.NONE);

[Johnni Winther, 2013/01/10 07:09:55]

I don't think this kind is used anymore.

[ngeoffray, 2013/01/10 09:41:48]

As discussed, I'll leave it to you or another CL.

+  static const ElementKind UNRESOLVED =

[ahe, 2013/01/09 15:46:27]

Could you use ErroneousElement instead?

[Johnni Winther, 2013/01/10 07:09:55]

ErroneousElement has a different semantics in the backend, namely that a runtime
error should be produced for it. Therefore we need something else.

[ahe, 2013/01/10 07:32:07]

I don't see why. The element is only used by the mock compiler to compare for
identity. We should not add new classes and categories that aren't actually used
in production code.

[Johnni Winther, 2013/01/10 08:19:47]

You are right. I thought it was used by production code.

[ngeoffray, 2013/01/10 09:41:48]

Yes, Done.

+    const ElementKind('unresolved', ElementCategory.NONE);
 
   toString() => id;
 }
@@ -429,7 +431,16 @@
 }
 
 /**
- * An ambiguous element represent multiple elements accessible by the same name.
+ * An unresolved element represents a selector we did not try to
+ * resolve.
+ */
+class UnresolvedElement extends Element {
+  UnresolvedElement(SourceString name, Element enclosing)
+      : super(name, ElementKind.UNRESOLVED, enclosing);
+}
+
+/**
+ * An ambiguous element represents multiple elements accessible by the same name.

[Johnni Winther, 2013/01/10 07:09:55]

Long line.

[ngeoffray, 2013/01/10 09:41:48]

Done.

  *
  * Ambiguous elements are created during handling of import/export scopes. If an
  * ambiguous element is encountered during resolution a warning/error should be