Make dart:dom implementation types private so they don't muddle the docs.

client/dom/generated/src/frog/Rect.dart

Index: client/dom/generated/src/frog/Rect.dart
diff --git a/client/dom/generated/src/frog/Rect.dart b/client/dom/generated/src/frog/Rect.dart
index 2b87f0ae936b614c5deef137c71404d40e1ca7a4..97e7ecb431f53f45b240e9989411a3a7ffb4307d 100644
--- a/client/dom/generated/src/frog/Rect.dart
+++ b/client/dom/generated/src/frog/Rect.dart
@@ -1,11 +1,11 @@
 
-class RectJs extends DOMTypeJs implements Rect native "*Rect" {
+class _RectJs extends _DOMTypeJs implements Rect native "*Rect" {
 
-  CSSPrimitiveValueJs get bottom() native "return this.bottom;";
+  _CSSPrimitiveValueJs get bottom() native "return this.bottom;";
 
-  CSSPrimitiveValueJs get left() native "return this.left;";
+  _CSSPrimitiveValueJs get left() native "return this.left;";
 
-  CSSPrimitiveValueJs get right() native "return this.right;";
+  _CSSPrimitiveValueJs get right() native "return this.right;";
 
-  CSSPrimitiveValueJs get top() native "return this.top;";
+  _CSSPrimitiveValueJs get top() native "return this.top;";
 }