Updating Clipboard.setDragImage to accept elements.

tools/dom/idl/dart/dart.idl

 // This file introduces / supplements and forces Dart declarations.
 
 [Supplemental,
  Constructor]
 interface AudioContext {
   // TODO(ager): Auto-generate this custom method when the info about retaining
   // typed arrays is in the IDL.
   [Custom] void decodeAudioData(ArrayBuffer audioData, AudioBufferCallback successCallback, AudioBufferCallback errorCallback);
 };
 
 [Supplemental]
 interface WaveShaperNode {
   // TODO(ager): Auto-generate this custom method when the info about retaining
   // typed arrays is in the IDL.
   [CustomSetter] attribute Float32Array curve;
 };
 
 [Supplemental]
 interface AudioParam {
   // TODO(ager): Auto-generate this custom method when the info about retaining
   // typed arrays is in the IDL.
   [Custom] void setValueCurveAtTime(Float32Array values, float time, float duration);
 };
 
 [Supplemental]
+interface Clipboard {
+  [Suppressed] void setDragImage(HTMLImageElement image, long x, long y);
+  [Custom] void setDragImage(Element element, long x, long y);
+};
+
+[Supplemental]
 interface Document {
   [Suppressed] DOMObject getCSSCanvasContext(DOMString contextId, DOMString name, long width, long height);
   CanvasRenderingContext getCSSCanvasContext(DOMString contextId, DOMString name, long width, long height);
 };
 
 [Supplemental]
 interface ScriptProcessorNode {
   [Suppressed] attribute EventListener onaudioprocess;
   [Custom] void _setEventListener(EventListener eventListener);
 };
@@ skipping 256 matching lines @@
 [Suppressed]
 interface InspectorFrontendHost {};
 
 
 [Suppressed]
 interface JavaScriptCallFrame {};
 
 
 [Suppressed]
 interface Entity {};