Drag and drop improvements on X11.

ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc

Index: ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc b/ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc
index 660c9e85f8a146e5dc63e0b470a2b0d90e946cdf..0dc489ce3e3a7c0c5057566dd2b13f297a407ea4 100644
--- a/ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc
+++ b/ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc
@@ -329,6 +329,13 @@ void DesktopDragDropClientAuraX11::X11DragContext::OnSelectionNotify(
     return;
   }
   DCHECK(drag_drop_client_);
+
+  if (event.property == None) {
+    // The selection conversion failed. This actually happens in real life.
+    // http://crbug.com/628099

[Elliot Glaysher, 2016/09/27 23:39:10]

Should this be an early return or a check around adding the incoming data to
|fetched_targets_|?

If we fail one selection conversion, do we want to fail all of them? If we fail
here, we aren't going to RequestNextTarget(), and we will never return data back
to our |drag_drop_client_|.

(This is actually a question and not rhetoric; I don't immediately know the
answer here.)

[pwnall, 2016/09/30 20:02:17]

Done.
Thank you very much for asking this question! You're right!

I tried implementing this fix, and I still couldn't get text to drag from
LibreOffice. However, after reading the relevant specs, I realized that we had
another bug -- we were calling XConvertSelection with a "now" timestamp, instead
of using the time stamp from the last XdndPosition message. Fixing that bug got
the drag to happen.

For posterity: note that fixing time stamps is not sufficient to get the drop
from LibreOffice working. LibreOffice exposes 6 data formats, but fails when we
ask for one of them. The other 5 formats work (when XConvertSelection receives
the correct time stamp), and that's enough for us to complete the drop.

+    return;
+  }
+
   DCHECK_EQ(event.property, atom_cache_->GetAtom(kChromiumDragReciever));
 
   scoped_refptr<base::RefCountedMemory> data;