fix for #27791. assume that any drag motion events are not valid drop targets unless someone explicitly sets the canDrop = true in the JS event handler. this makes dragging feedback correct on linux. r=pavlov

widget/public/nsIDragSessionGTK.h

@@ -39,7 +39,10 @@ class nsIDragSessionGTK : public nsISupports {
   NS_IMETHOD SetLastContext  (GtkWidget      *aWidget,
                               GdkDragContext *aContext,
                               guint           aTime) = 0;
-  NS_IMETHOD UpdateDragStatus(GtkWidget      *aWidget,
+  NS_IMETHOD StartDragMotion (GtkWidget      *aWidget,
+                              GdkDragContext *aContext,
+                              guint           aTime) = 0;
+  NS_IMETHOD EndDragMotion   (GtkWidget      *aWidget,
                               GdkDragContext *aContext,
                               guint           aTime) = 0;
   NS_IMETHOD SetDataReceived (GtkWidget         *aWidget,

widget/src/gtk/nsDragService.cpp

@@ -341,12 +341,25 @@ NS_IMETHODIMP nsDragService::SetLastContext  (GtkWidget          *aWidget,
   return NS_OK;
 }
 
-NS_IMETHODIMP nsDragService::UpdateDragStatus(GtkWidget          *aWidget,
-                                              GdkDragContext     *aContext,
-                                              guint               aTime)
+NS_IMETHODIMP nsDragService::StartDragMotion(GtkWidget      *aWidget,
+                                             GdkDragContext *aContext,
+                                             guint           aTime)
 {
 #ifdef DEBUG_DD
-  g_print("UpdateDragStatus: %d\n", mCanDrop);
+  g_print("StartDragMotion\n");
+#endif
+  // set our drop target to false since we probably won't get
+  // notification if there's no JS DND listener.
+  mCanDrop = PR_FALSE;
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsDragService::EndDragMotion(GtkWidget      *aWidget,
+                                           GdkDragContext *aContext,
+                                           guint           aTime)
+{
+#ifdef DEBUG_DD
+  g_print("EndDragMotion: %d\n", mCanDrop);
 #endif
   if (mCanDrop) 
     gdk_drag_status(aContext, GDK_ACTION_COPY, aTime);

widget/src/gtk/nsDragService.h

@@ -59,9 +59,12 @@ public:
   NS_IMETHOD SetLastContext  (GtkWidget          *aWidget,
                               GdkDragContext     *aContext,
                               guint               aTime);
-  NS_IMETHOD UpdateDragStatus(GtkWidget          *aWidget,
-                              GdkDragContext     *aContext,
-                              guint               aTime);
+  NS_IMETHOD StartDragMotion (GtkWidget      *aWidget,
+                              GdkDragContext *aContext,
+                              guint           aTime);
+  NS_IMETHOD EndDragMotion   (GtkWidget      *aWidget,
+                              GdkDragContext *aContext,
+                              guint           aTime);
   NS_IMETHOD SetDataReceived (GtkWidget          *aWidget,
                               GdkDragContext     *context,
                               gint                x,

widget/src/gtk/nsWidget.cpp

@@ -2973,7 +2973,7 @@ void nsWidget::UpdateDragContext(GtkWidget *aWidget, GdkDragContext *aGdkDragCon
 }
 
 /* virtual */
-void nsWidget::UpdateDragStatus(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime)
+void nsWidget::StartDragMotion(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime)
 {
   // make sure that we tell the drag manager what the hell is going on.
   nsCOMPtr<nsIDragService> dragService;
@@ -2989,7 +2989,27 @@ void nsWidget::UpdateDragStatus(GtkWidget *aWidget, GdkDragContext *aGdkDragCont
   if (!dragServiceGTK) {
     return;
   }
-  dragServiceGTK->UpdateDragStatus(aWidget, aGdkDragContext, aTime);
+  dragServiceGTK->StartDragMotion(aWidget, aGdkDragContext, aTime);
+}
+
+/* virtual */
+void nsWidget::EndDragMotion(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime)
+{
+  // make sure that we tell the drag manager what the hell is going on.
+  nsCOMPtr<nsIDragService> dragService;
+  nsresult rv = nsServiceManager::GetService(kCDragServiceCID,
+                                             nsIDragService::GetIID(),
+                                             (nsISupports **)&dragService);
+  if (NS_FAILED(rv)) {
+    g_print("*** warning: failed to get the drag service. this is a _bad_ thing.\n");
+    return;
+  }
+  nsCOMPtr<nsIDragSessionGTK> dragServiceGTK;
+  dragServiceGTK = do_QueryInterface(dragService);
+  if (!dragServiceGTK) {
+    return;
+  }
+  dragServiceGTK->EndDragMotion(aWidget, aGdkDragContext, aTime);
 }
 
 #ifdef NS_DEBUG

widget/src/gtk/nsWidget.h

@@ -202,7 +202,8 @@ public:
 protected:
 
   virtual void UpdateDragContext(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime);
-  virtual void UpdateDragStatus(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime);
+  virtual void StartDragMotion(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime);
+  virtual void EndDragMotion(GtkWidget *aWidget, GdkDragContext *aGdkDragContext, guint aTime);
 
   virtual void InitCallbacks(char * aName = nsnull);
 

widget/src/gtk/nsWindow.cpp

@@ -1357,6 +1357,9 @@ nsWindow::OnToplevelDragMotion     (GtkWidget      *aWidget,
     innerMostWidget->OnDragEnterSignal(aDragContext, x, y, aTime);
   }
 
+  // notify the drag service that we are starting a drag motion.
+  StartDragMotion(aWidget, aDragContext, aTime);
+
   nsMouseEvent event;
 
   event.message = NS_DRAGDROP_OVER;
@@ -1373,8 +1376,8 @@ nsWindow::OnToplevelDragMotion     (GtkWidget      *aWidget,
 
   innerMostWidget->Release();
 
-  // now that we've dispatched the signal, update the drag context
-  UpdateDragStatus(aWidget, aDragContext, aTime);
+  // we're done with the drag motion event.  notify the drag service.
+  EndDragMotion(aWidget, aDragContext, aTime);
 }
 
 void