Bug 1720804 - Part 1: Move majority of the display list code inside mozilla namespace r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D120041

layout/xul/tree/nsTreeBodyFrame.cpp

@@ -2480,6 +2480,8 @@ nsresult nsTreeBodyFrame::HandleEvent(nsPresContext* aPresContext,
   return NS_OK;
 }
 
+namespace mozilla {
+
 class nsDisplayTreeBody final : public nsPaintedDisplayItem {
  public:
   nsDisplayTreeBody(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
@@ -2541,6 +2543,8 @@ class nsDisplayTreeBody final : public nsPaintedDisplayItem {
   }
 };
 
+}  // namespace mozilla
+
 #ifdef XP_MACOSX
 static bool IsInSourceList(nsIFrame* aFrame) {
   for (nsIFrame* frame = aFrame; frame;