Fix deadlock between UI thread and drag and drop thread on Windows.

content/browser/web_contents/web_drag_source_win.h

Index: content/browser/web_contents/web_drag_source_win.h
diff --git a/content/browser/web_contents/web_drag_source_win.h b/content/browser/web_contents/web_drag_source_win.h
index 898f3c3ada546fd21966d763e5dd9d0993247d63..1aa347fe9925b331b56385106014cbc7efdbb220 100644
--- a/content/browser/web_contents/web_drag_source_win.h
+++ b/content/browser/web_contents/web_drag_source_win.h
@@ -12,6 +12,10 @@
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/point.h"
 
+namespace ui {
+class OSExchangeData;
+}  // namespace ui
+
 namespace content {
 class RenderViewHost;
 class WebContents;
@@ -33,6 +37,10 @@ class WebDragSource : public ui::DragSourceWin,
                        const NotificationDetails& details);
 
   void set_effect(DWORD effect) { effect_ = effect; }
+  // Used to set the active data object for the current drag operation. The
+  // caller must ensure that |data| is not destroyed before the nested drag loop
+  // terminates.
+  void set_data(ui::OSExchangeData* data) { data_ = data; }
 
  protected:
   // ui::DragSourceWin
@@ -60,6 +68,8 @@ class WebDragSource : public ui::DragSourceWin,
 
   DWORD effect_;
 
+  ui::OSExchangeData* data_;
+
   DISALLOW_COPY_AND_ASSIGN(WebDragSource);
 };