Change inference element invariants

pkg/compiler/lib/src/common_elements.dart

Index: pkg/compiler/lib/src/common_elements.dart
diff --git a/pkg/compiler/lib/src/common_elements.dart b/pkg/compiler/lib/src/common_elements.dart
index 760f5d16c2dc7a90abdfcf26d468bf97fe1a9512..d508e555f0d37ef351e85baf0794d747dbaa3411 100644
--- a/pkg/compiler/lib/src/common_elements.dart
+++ b/pkg/compiler/lib/src/common_elements.dart
@@ -1144,6 +1144,8 @@ class CommonElements {
     _ensureExpectAnnotations();
     return _expectAssumeDynamicClass;
   }
+
+  bool isForeign(MemberEntity element) => element.library == foreignLibrary;
 }
 
 /// Interface for accessing libraries, classes and members.