Analyzer: Don't allow extending or implementing Null.

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/resolver/TypeProvider.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/resolver/TypeProvider.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/resolver/TypeProvider.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/resolver/TypeProvider.java
index 6b4042d102dca086f91913016c7b591187c99247..8858bea5af146c70068a5fec8bc292a23114cf77 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/resolver/TypeProvider.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/resolver/TypeProvider.java
@@ -1,11 +1,11 @@
 /*
  * Copyright (c) 2013, the Dart project authors.
- * 
+ *
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
- * 
+ *
  * http://www.eclipse.org/legal/epl-v10.html
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software distributed under the License
  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
  * or implied. See the License for the specific language governing permissions and limitations under
@@ -19,104 +19,111 @@ import com.google.dart.engine.type.Type;
 /**
  * The interface {@code TypeProvider} defines the behavior of objects that provide access to types
  * defined by the language.
- * 
+ *
  * @coverage dart.engine.resolver
  */
 public interface TypeProvider {
   /**
+   * Return the type representing the built-in type 'Null'.
+   *
+   * @return the type representing the built-in type 'null'
+   */
+  public InterfaceType getNullType();
+
+  /**
    * Return the type representing the built-in type 'bool'.
-   * 
+   *
    * @return the type representing the built-in type 'bool'
    */
   public InterfaceType getBoolType();
 
   /**
    * Return the type representing the type 'bottom'.
-   * 
+   *
    * @return the type representing the type 'bottom'
    */
   public Type getBottomType();
 
   /**
    * Return the type representing the built-in type 'double'.
-   * 
+   *
    * @return the type representing the built-in type 'double'
    */
   public InterfaceType getDoubleType();
 
   /**
    * Return the type representing the built-in type 'dynamic'.
-   * 
+   *
    * @return the type representing the built-in type 'dynamic'
    */
   public Type getDynamicType();
 
   /**
    * Return the type representing the built-in type 'Function'.
-   * 
+   *
    * @return the type representing the built-in type 'Function'
    */
   public InterfaceType getFunctionType();
 
   /**
    * Return the type representing the built-in type 'int'.
-   * 
+   *
    * @return the type representing the built-in type 'int'
    */
   public InterfaceType getIntType();
 
   /**
    * Return the type representing the built-in type 'List'.
-   * 
+   *
    * @return the type representing the built-in type 'List'
    */
   public InterfaceType getListType();
 
   /**
    * Return the type representing the built-in type 'Map'.
-   * 
+   *
    * @return the type representing the built-in type 'Map'
    */
   public InterfaceType getMapType();
 
   /**
    * Return the type representing the built-in type 'num'.
-   * 
+   *
    * @return the type representing the built-in type 'num'
    */
   public InterfaceType getNumType();
 
   /**
    * Return the type representing the built-in type 'Object'.
-   * 
+   *
    * @return the type representing the built-in type 'Object'
    */
   public InterfaceType getObjectType();
 
   /**
    * Return the type representing the built-in type 'StackTrace'.
-   * 
+   *
    * @return the type representing the built-in type 'StackTrace'
    */
   public InterfaceType getStackTraceType();
 
   /**
    * Return the type representing the built-in type 'String'.
-   * 
+   *
    * @return the type representing the built-in type 'String'
    */
   public InterfaceType getStringType();
 
   /**
    * Return the type representing the built-in type 'Symbol'.
-   * 
+   *
    * @return the type representing the built-in type 'Symbol'
    */
   public InterfaceType getSymbolType();
 
   /**
    * Return the type representing the built-in type 'Type'.
-   * 
+   *
    * @return the type representing the built-in type 'Type'
    */
   public InterfaceType getTypeType();