Fixing analyzer warnings on overloading == but not get hashCode.

tools/dom/src/Rectangle.dart

 // Copyright (c) 2013, 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.
 
 part of html;
 
 /**
  * A class for representing two-dimensional rectangles.
  */
 class Rect {
@@ skipping 36 matching lines @@
   String toString() {
     return '($left, $top, $width, $height)';
   }
 
   bool operator ==(other) {
     if (other is !Rect) return false;
     return left == other.left && top == other.top && width == other.width &&
         height == other.height;
   }
 
+  int get hashCode => JenkinsSmiHash.hash4(left.hashCode, top.hashCode,
+      width.hashCode, height.hashCode);
+
   /**
    * Computes the intersection of this rectangle and the rectangle parameter.
    * Returns null if there is no intersection.
    */
   Rect intersection(Rect rect) {
     var x0 = max(left, rect.left);
     var x1 = min(left + width, rect.left + rect.width);
 
     if (x0 <= x1) {
       var y0 = max(top, rect.top);
@@ skipping 59 matching lines @@
    * Truncates coordinates to integers and returns the result as a new
    * rectangle.
    */
   Rect toInt() => new Rect(left.toInt(), top.toInt(), width.toInt(),
       height.toInt());
 
   Point get topLeft => new Point(this.left, this.top);
   Point get bottomRight => new Point(this.left + this.width,
       this.top + this.height);
 }