Remove unused API.

dart/sdk/lib/_internal/compiler/implementation/types/union_type_mask.dart

Index: dart/sdk/lib/_internal/compiler/implementation/types/union_type_mask.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/types/union_type_mask.dart b/dart/sdk/lib/_internal/compiler/implementation/types/union_type_mask.dart
index de7fc8fba368ed49b278c029cda719f12971341a..b632e9bdc5eb38d1dc0a067a8e931d34d49bc370 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/types/union_type_mask.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/types/union_type_mask.dart
@@ -219,10 +219,6 @@ class UnionTypeMask implements TypeMask {
     });
   }
 
-  bool containsOnlyNull(Compiler compiler) {
-    return disjointMasks.every((mask) => mask.containsOnlyNull(compiler));
-  }
-
   bool containsOnlyBool(Compiler compiler) {
     return disjointMasks.every((mask) => mask.containsOnlyBool(compiler));
   }
@@ -249,15 +245,6 @@ class UnionTypeMask implements TypeMask {
 
   ClassElement singleClass(Compiler compiler) => null;
 
-  Iterable<ClassElement> containedClasses(Compiler compiler) {
-    return disjointMasks.expand(
-        (TypeMask mask) => mask.containedClasses(compiler));
-  }
-
-  bool understands(Selector selector, Compiler compiler) {
-    return disjointMasks.any((e) => e.understands(selector, compiler));
-  }
-
   bool needsNoSuchMethodHandling(Selector selector, Compiler compiler) {
     return disjointMasks.any(
         (e) => e.needsNoSuchMethodHandling(selector, compiler));