Rename ReceiverMask and ReceiverMaskSet and update comments.

pkg/compiler/lib/src/js_emitter/class_stub_generator.dart

Index: pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
diff --git a/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
index c8d478b68ec8eaccf5f649ae211f57b878c8d0d7..1ea0be0b7b6d4d1153f84ecf3c39fe4f8e17d3c9 100644
--- a/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
@@ -48,7 +48,7 @@ class ClassStubGenerator {
    * Invariant: [member] must be a declaration element.
    */
   Map<jsAst.Name, jsAst.Expression> generateCallStubsForGetter(
-      Element member, Map<Selector, ReceiverMaskSet> selectors) {
+      Element member, Map<Selector, SelectorConstraints> selectors) {
     assert(invariant(member, member.isDeclaration));
 
     // If the method is intercepted, the stub gets the
@@ -124,9 +124,9 @@ class ClassStubGenerator {
     }
 
     void addNoSuchMethodHandlers(String ignore,
-                                 Map<Selector, ReceiverMaskSet> selectors) {
+                                 Map<Selector, SelectorConstraints> selectors) {
       for (Selector selector in selectors.keys) {
-        ReceiverMaskSet maskSet = selectors[selector];
+        SelectorConstraints maskSet = selectors[selector];
         if (maskSet.needsNoSuchMethodHandling(selector, compiler.world)) {
           jsAst.Name jsName = namer.invocationMirrorInternalName(selector);
           jsNames[jsName] = selector;