Bug 376238, add a pref to disable drag images, r=sr=roc

modules/libpref/src/init/all.js

@@ -197,6 +197,9 @@ pref("view_source.wrap_long_lines", false);
 // dispatch left clicks only to content in browser (still allows clicks to chrome/xul)
 pref("nglayout.events.dispatchLeftClickOnly", true);
 
+// whether or not to draw images while dragging
+pref("nglayout.enable_drag_images", true);
+
 // whether or not to use xbl form controls
 pref("nglayout.debug.enable_xbl_forms", false);
 

widget/src/xpwidgets/nsBaseDragService.cpp

@@ -69,6 +69,7 @@
 #include "nsIViewObserver.h"
 #include "nsRegion.h"
 #include "nsGUIEvent.h"
+#include "nsIPrefService.h"
 
 #ifdef MOZ_CAIRO_GFX
 #include "gfxContext.h"
@@ -76,6 +77,8 @@
 
 #endif
 
+#define DRAGIMAGES_PREF "nglayout.enable_drag_images"
+
 NS_IMPL_ADDREF(nsBaseDragService)
 NS_IMPL_RELEASE(nsBaseDragService)
 NS_IMPL_QUERY_INTERFACE2(nsBaseDragService, nsIDragService, nsIDragSession)
@@ -412,8 +415,14 @@ nsBaseDragService::DrawDrag(nsIDOMNode* aDOMNode,
   if (!presShell)
     return NS_ERROR_FAILURE;
 
+  // check if drag images are disabled
+  PRBool enableDragImages = PR_TRUE;
+  nsCOMPtr<nsIPrefBranch> prefs(do_GetService(NS_PREFSERVICE_CONTRACTID));
+  if (prefs)
+    prefs->GetBoolPref(DRAGIMAGES_PREF, &enableDragImages);
+
   // didn't want an image, so just set the screen rectangle to the frame size
-  if (!mHasImage) {
+  if (!enableDragImages || !mHasImage) {
     // if a region was specified, set the screen rectangle to the area that
     // the region occupies
     if (aRegion) {