Drag and drop improvements on X11.

ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/widget/desktop_aura/desktop_drag_drop_client_aurax11.h"
 
 #include <X11/Xatom.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 311 matching lines @@
 }
 
 void DesktopDragDropClientAuraX11::X11DragContext::OnSelectionNotify(
     const XSelectionEvent& event) {
   if (!waiting_to_handle_position_) {
     // A misbehaved window may send SelectionNotify without us requesting data
     // via XConvertSelection().
     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;
   ::Atom type = None;
   if (ui::GetRawBytesOfProperty(local_window_, event.property,
                                 &data, NULL, &type)) {
     fetched_targets_.Insert(event.target, data);
   }
 
   if (!unfetched_targets_.empty()) {
@@ skipping 883 matching lines @@
     for (int x = 0; x < in_bitmap->width(); ++x) {
       if (SkColorGetA(in_row[x]) > kMinAlpha)
         return true;
     }
   }
 
   return false;
 }
 
 }  // namespace views