Bug 1419546 - Consider mLayer in nsDisplayTableBackgroundImage::GetPerFrameKey(). r=mattwoodrow

MozReview-Commit-ID: Bqk0U4REESW

--HG--
extra : rebase_source : 6519c6df50d282cbeff42b414ac13578347e8586

layout/painting/nsDisplayList.h

@@ -3824,7 +3824,8 @@ public:
   nsDisplayTableBackgroundImage(const InitData& aInitData, nsIFrame* aCellFrame);
 
   virtual uint32_t GetPerFrameKey() const override {
-    return (static_cast<uint8_t>(mTableType) << TYPE_BITS) |
+    return (mLayer << (TYPE_BITS + static_cast<uint8_t>(TableTypeBits::COUNT))) |
+           (static_cast<uint8_t>(mTableType) << TYPE_BITS) |
            nsDisplayItem::GetPerFrameKey();
   }