Change TypeMask.base to be a ClassElement.

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

Index: sdk/lib/_internal/compiler/implementation/universe/universe.dart
diff --git a/sdk/lib/_internal/compiler/implementation/universe/universe.dart b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
index 1bcf5141a67f3418fefc0f09258f5c12cc649200..e0b1548005ffe72757d3e1c847706d05915a163e 100644
--- a/sdk/lib/_internal/compiler/implementation/universe/universe.dart
+++ b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
@@ -638,13 +638,13 @@ class TypedSelector extends Selector {
     return result;
   }
 
-  factory TypedSelector.exact(DartType base, Selector selector)
+  factory TypedSelector.exact(ClassElement base, Selector selector)
       => new TypedSelector(new TypeMask.exact(base), selector);
 
-  factory TypedSelector.subclass(DartType base, Selector selector)
+  factory TypedSelector.subclass(ClassElement base, Selector selector)
       => new TypedSelector(new TypeMask.subclass(base), selector);
 
-  factory TypedSelector.subtype(DartType base, Selector selector)
+  factory TypedSelector.subtype(ClassElement base, Selector selector)
       => new TypedSelector(new TypeMask.subtype(base), selector);
 
   bool appliesUnnamed(Element element, Compiler compiler) {