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

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

 
-class ClipboardJs extends DOMTypeJs implements Clipboard native "*Clipboard" {
+class _ClipboardJs extends _DOMTypeJs implements Clipboard native "*Clipboard" {
 
   String get dropEffect() native "return this.dropEffect;";
 
   void set dropEffect(String value) native "this.dropEffect = value;";
 
   String get effectAllowed() native "return this.effectAllowed;";
 
   void set effectAllowed(String value) native "this.effectAllowed = value;";
 
-  FileListJs get files() native "return this.files;";
+  _FileListJs get files() native "return this.files;";
 
-  DataTransferItemListJs get items() native "return this.items;";
+  _DataTransferItemListJs get items() native "return this.items;";
 
   List get types() native "return this.types;";
 
   void clearData([String type = null]) native;
 
   void getData(String type) native;
 
   bool setData(String type, String data) native;
 
-  void setDragImage(HTMLImageElementJs image, int x, int y) native;
+  void setDragImage(_HTMLImageElementJs image, int x, int y) native;
 }