Move Rectangle and Point into dart:math.

tools/dom/templates/html/impl/impl_Element.darttemplate

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index 100e017726554ec206a76588c7048e92ce635435..0909ffaf5b86425495b02126de7a527a1f297156 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -666,12 +666,14 @@ $(ANNOTATIONS)abstract class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   /**
    * Gets the position of this element relative to the client area of the page.
    */
-  Rect get client => new Rect(clientLeft, clientTop, clientWidth, clientHeight);
+  Rectangle get client => new Rectangle(clientLeft, clientTop, clientWidth, 
+      clientHeight);
 
   /**
    * Gets the offset of this element relative to its offsetParent.
    */
-  Rect get offset => new Rect(offsetLeft, offsetTop, offsetWidth, offsetHeight);
+  Rectangle get offset => new Rectangle(offsetLeft, offsetTop, offsetWidth, 
+      offsetHeight);
 
   /**
    * Adds the specified text after the last child of this element.