Remove unused API.

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

Index: dart/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/types/type_mask.dart b/dart/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
index e99a8f41082af3be806cd64bf76d3fc4f80a704c..24b60b4725d4867505b5f7fd576e1b071b14be68 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/types/type_mask.dart
@@ -57,7 +57,6 @@ abstract class TypeMask {
   bool containsOnlyInt(Compiler compiler);
   bool containsOnlyDouble(Compiler compiler);
   bool containsOnlyNum(Compiler compiler);
-  bool containsOnlyNull(Compiler compiler);
   bool containsOnlyBool(Compiler compiler);
   bool containsOnlyString(Compiler compiler);
   bool containsOnly(ClassElement element);
@@ -94,11 +93,6 @@ abstract class TypeMask {
   ClassElement singleClass(Compiler compiler);
 
   /**
-   * Returns the classes this type mask can be.
-   */
-  Iterable<ClassElement> containedClasses(Compiler compiler);
-
-  /**
    * Returns a type mask representing the union of [this] and [other].
    */
   TypeMask union(TypeMask other, Compiler compiler);
@@ -109,11 +103,6 @@ abstract class TypeMask {
   TypeMask intersection(TypeMask other, Compiler compiler);
 
   /**
-   * Returns whether this [TypeMask] understands [selector].
-   */
-  bool understands(Selector selector, Compiler compiler);
-
-  /**
    * Returns whether this [TypeMask] applied to [selector] can hit a
    * [noSuchMethod].
    */