Fix crash when the source browser window is deleted during a drag

ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc

Index: ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc
diff --git a/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc b/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc
index f471b3254bf1825823c32f48e1c72e1105b0d757..fc581e201d781c71844f10973ed056e015a68bad 100644
--- a/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc
+++ b/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc
@@ -17,11 +17,13 @@ DesktopDragDropClientWin::DesktopDragDropClientWin(
     aura::Window* root_window,
     HWND window)
     : drag_drop_in_progress_(false),
-      drag_operation_(0) {
+      drag_operation_(0),
+      weak_factory_(this) {
   drop_target_ = new DesktopDropTargetWin(root_window, window);
 }
 
 DesktopDragDropClientWin::~DesktopDragDropClientWin() {
+  DragCancel();
 }
 
 int DesktopDragDropClientWin::StartDragAndDrop(
@@ -34,13 +36,18 @@ int DesktopDragDropClientWin::StartDragAndDrop(
   drag_drop_in_progress_ = true;
   drag_operation_ = operation;
 
+  base::WeakPtr<DesktopDragDropClientWin> alive(weak_factory_.GetWeakPtr());
+
   drag_source_ = new ui::DragSourceWin;
+  scoped_refptr<ui::DragSourceWin> drag_source_copy = drag_source_;
+
   DWORD effect;
   HRESULT result = DoDragDrop(
       ui::OSExchangeDataProviderWin::GetIDataObject(data), drag_source_.get(),
       ui::DragDropTypes::DragOperationToDropEffect(operation), &effect);
 
-  drag_drop_in_progress_ = false;
+  if (alive)
+    drag_drop_in_progress_ = false;
 
   if (result != DRAGDROP_S_DROP)
     effect = DROPEFFECT_NONE;
@@ -57,7 +64,8 @@ void DesktopDragDropClientWin::Drop(aura::Window* target,
 }
 
 void DesktopDragDropClientWin::DragCancel() {
-  drag_source_->CancelDrag();
+  if (drag_drop_in_progress_)

[sky, 2014/12/15 20:44:13]

Should this be a DCHECK?

[pkotwicz, 2014/12/15 21:54:11]

In patch set #2, I moved the check to the destructor

+    drag_source_->CancelDrag();
   drag_operation_ = 0;
 }