aura: Add flag to indicate if a drag session is started with touch or mouse.

ash/drag_drop/drag_drop_controller.cc

Index: ash/drag_drop/drag_drop_controller.cc
diff --git a/ash/drag_drop/drag_drop_controller.cc b/ash/drag_drop/drag_drop_controller.cc
index 01788dd08822d220da04054f551d6a4c5576ddf5..8cfaec2cb84895514f1e73abbd4192db340d09aa 100644
--- a/ash/drag_drop/drag_drop_controller.cc
+++ b/ash/drag_drop/drag_drop_controller.cc
@@ -56,10 +56,13 @@ DragDropController::~DragDropController() {
     drag_image_.reset();
 }
 
-int DragDropController::StartDragAndDrop(const ui::OSExchangeData& data,
-                                         aura::RootWindow* root_window,
-                                         const gfx::Point& root_location,
-                                         int operation) {
+int DragDropController::StartDragAndDrop(
+    const ui::OSExchangeData& data,
+    aura::RootWindow* root_window,
+    aura::Window* source_window,
+    const gfx::Point& root_location,
+    int operation,
+    ui::DragDropTypes::DragEventSource source) {
   DCHECK(!IsDragDropInProgress());
 
   drag_drop_tracker_.reset(new DragDropTracker);