Fix a renderer crash when dragging quickly over tab contents.

We were expecting to receive GTK+ events in the following order:
  drag-motion
  drag-data-received
  drag-leave
but in some cases, we don't get the drag-data-received event (e.g.,
if the user is moving the mouse quickly). If that happens, don't send
a DragLeave event to the renderer since it doesn't think we're in a
drag.

BUG=129446
TEST=Open 2 chrome windows, quickly drag a file from the desktop over both
  windows. This should not crash.


Review URL: https://chromiumcodereview.appspot.com/10704144

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@146016 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/web_contents/web_drag_dest_gtk.cc

@@ -91,7 +91,6 @@ void WebDragDestGtk::UpdateDragStatus(WebDragOperation operation) {
 
 void WebDragDestGtk::DragLeave() {
   GetRenderViewHost()->DragTargetDragLeave();
-
   if (delegate())
     delegate()->OnDragLeave();
 
@@ -270,6 +269,12 @@ void WebDragDestGtk::OnDragLeave(GtkWidget* sender, GdkDragContext* context,
   // as an enter.
   context_ = NULL;
 
+  // Sometimes we get a drag-leave event before getting a drag-data-received
+  // event. In that case, we don't want to bother the renderer with a
+  // DragLeave event.
+  if (data_requests_ != 0)
+    return;
+
   // When GTK sends us a drag-drop signal, it is shortly (and synchronously)
   // preceded by a drag-leave. The renderer doesn't like getting the signals
   // in this order so delay telling it about the drag-leave till we are sure