Add documentation to the Object class in the core library.

lib/core/object.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Everything in Dart is an [Object].
  */
 class Object {
+  /**
+   * Creates a new [Object] instance.
+   *
+   * [Object] instances have no meaningful state, and are only useful
+   * through their identity. An [Object] instance is equal to itself
+   * only.
+   */
   const Object();
 
+  /**
+   * The equality operator.
+   *
+   * The default behavior for all [Object]s is to return true if and
+   * only if [:this:] and [other] are the same object.
+   *
+   * If a subclass overrides the equality operator it should override
+   * the [hashCode] method as well to maintain consistency.
+   */
   bool operator ==(other) => identical(this, other);
 
+  /**
+   * Get a hash code for this object.
+   *
+   * All objects have hash codes. Hash codes are guaranteed to be the
+   * same for objects that are equal when compared using the equality
+   * operator [:==:]. Other than that there are no guarantees about
+   * the hash codes. They will not be consistent between runs and
+   * there are no distribution guarantees.
+   *
+   * If a subclass overrides [hashCode] it should override the
+   * equality operator as well to maintain consistency.
+   */
   external int hashCode();
 
+  /**
+   * Returns a string representation of this object.
+   */
   external String toString();
 
-  external void noSuchMethod(String name, List args);
+  /**
+   * [noSuchMethod] is invoked when users invoke a non-existant method
+   * on an object. The name of the method and the arguments of the
+   * invocation are passed to [noSuchMethod]. If [noSuchMethod]
+   * returns a value, that value becomes the result of the original
+   * invocation.
+   *
+   * The default behavior of [noSuchMethod] is to throw a
+   * [noSuchMethodError].
+   */
+  external Dynamic noSuchMethod(String name, List args);
 
+  /**
+   * Returns a representation of the runtime type of the object.
+   */
   external Type runtimeType();
 }
 
+/**
+ * Representation of a type.
+ */
 abstract class Type {}
 
 /**
  * Check whether two references are to the same object.
  */
 bool identical(Object a, Object b) => a === b;