fix bug #41998. reset mouse motion variables whenever a drag is started. this should fix the lack of UI events after a drag. r=bryner, a=brendan

widget/src/gtk/nsDragService.cpp

@@ -28,6 +28,7 @@
 #include "nsVoidArray.h"
 #include "nsXPIDLString.h"
 #include "nsPrimitiveHelpers.h"
+#include "nsWidget.h"
 #include <gtk/gtkinvisible.h>
 #include <gdk/gdkx.h>
 
@@ -144,6 +145,9 @@ nsDragService::InvokeDragSession (nsIDOMNode *aDOMNode,
     gdk_event.button.x_root = 0;
     gdk_event.button.y_root = 0;
 
+    // before we start our drag, give the widget code a chance to
+    // clean up any state.
+    nsWidget::DragStarted();
     // start our drag.
     GdkDragContext *context = gtk_drag_begin(mHiddenWidget,
                                              sourceList,

widget/src/gtk/nsWidget.cpp

@@ -117,6 +117,18 @@ void nsWidget::GetLastEventTime(guint32 *aTime)
     *aTime = sLastEventTime;
 }
 
+void nsWidget::DragStarted(void)
+{
+  if (sButtonMotionTarget)
+  {
+    sButtonMotionTarget = nsnull;
+    sButtonMotionRootX = -1;
+    sButtonMotionRootY = -1;
+    sButtonMotionWidgetX = -1;
+    sButtonMotionWidgetY = -1;
+  }
+}
+
 #ifdef USE_XIM
 nsresult nsWidget::KillICSpotTimer ()
 {

widget/src/gtk/nsWidget.h

@@ -206,6 +206,11 @@ public:
   // the event handling code needs to let us know the time of the last event
   static void SetLastEventTime(guint32 aTime);
   static void GetLastEventTime(guint32 *aTime);
+
+  // inform the widget code that we are about to do a drag - it must
+  // release the sButtonMotionTarget if it is set.
+  static void DragStarted(void);
+
 protected:
 
   virtual void InitCallbacks(char * aName = nsnull);