Allow the cursor to warp even when a window is dragged

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index ed8ba9714e447beedae38df9426ce400c26ed6da..741dcde6f28d7c92ded6597e8eea3357769f689d 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -178,6 +178,15 @@ class ASH_EXPORT Shell : ash::CursorDelegate {
   // returns the primary root window only.
   static RootWindowList GetAllRootWindows();
 
+  // If |location_in_root| is inside |root_window|'s bounds, just returns a pair
+  // of |root_window| and |location_in_root| as-is. If |location_in_root| is
+  // outside the |root_window|, the function tries to find another root window
+  // where the cursor is on and returns a pair of the window and location in the
+  // window's coordinates.
+  static std::pair<aura::RootWindow*, gfx::Point> NormalizeLocationInDragEvent(
+    aura::RootWindow* root_window,
+    gfx::Point location_in_root);
+
   static aura::Window* GetContainer(aura::RootWindow* root_window,
                                     int container_id);