Revert "Split TypedSelector into Selector and TypeMask."

pkg/compiler/lib/src/types/union_type_mask.dart

Index: pkg/compiler/lib/src/types/union_type_mask.dart
diff --git a/pkg/compiler/lib/src/types/union_type_mask.dart b/pkg/compiler/lib/src/types/union_type_mask.dart
index f4c45e7148ce34053d6b087e9509838018dc0ea5..3b0f139e5ac04d353b9037e6bcc1ae621648ca24 100644
--- a/pkg/compiler/lib/src/types/union_type_mask.dart
+++ b/pkg/compiler/lib/src/types/union_type_mask.dart
@@ -311,12 +311,10 @@ class UnionTypeMask implements TypeMask {
     return disjointMasks.any((e) => e.canHit(element, selector, classWorld));
   }
 
-  Element locateSingleElement(Selector selector,
-                              TypeMask mask,
-                              Compiler compiler) {
+  Element locateSingleElement(Selector selector, Compiler compiler) {
     Element candidate;
     for (FlatTypeMask mask in disjointMasks) {
-      Element current = mask.locateSingleElement(selector, mask, compiler);
+      Element current = mask.locateSingleElement(selector, compiler);
       if (current == null) {
         return null;
       } else if (candidate == null) {