Bug 1361749: Initialize nsScrollbarFrame::{mIncrement, mSmoothScroll}. r=mats

MozReview-Commit-ID: 8rgUPNr24gF
Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>

layout/xul/nsScrollbarFrame.h

@@ -22,6 +22,8 @@ class nsScrollbarFrame final : public nsBoxFrame
 public:
   explicit nsScrollbarFrame(nsStyleContext* aContext)
     : nsBoxFrame(aContext, mozilla::LayoutFrameType::Scrollbar)
+    , mIncrement(0)
+    , mSmoothScroll(false)
     , mScrollbarMediator(nullptr)
   {}