Bug 78087. Propagate the canvas background to be the background of the entire viewport so it z-orders correctly in the viewport's stacking context. r+sr=dbaron

layout/generic/nsGfxScrollFrame.cpp

@@ -1392,7 +1392,8 @@ nsGfxScrollFrameInner::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   NS_ENSURE_SUCCESS(rv, rv);
   nsRect clip = frameClip + aBuilder->ToReferenceFrame(mOuter);
   // mScrolledFrame may have given us a background, e.g., the scrolled canvas
-  // frame below the viewport. If so, we want it to be clipped.
+  // frame below the viewport. If so, we want it to be clipped. We also want
+  // to end up on our BorderBackground list.
   // If we are the viewport scrollframe, then clip all our descendants (to ensure
   // that fixed-pos elements get clipped by us).
   rv = mOuter->OverflowClip(aBuilder, set, aLists, clip, PR_TRUE, mIsRoot);

layout/generic/nsViewportFrame.cpp

@@ -89,10 +89,12 @@ ViewportFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   // that display list construction is guaranteed to recurse into their
   // ancestors.
   MarkOutOfFlowChildrenForDisplayList(mFixedContainer.GetFirstChild(), aDirtyRect);
-  // Put the regular child in a pseudo-stack.
-  nsresult rv =
-    BuildDisplayListForNonBlockChildren(aBuilder, aDirtyRect, aLists,
-                                        DISPLAY_CHILD_FORCE_PSEUDO_STACKING_CONTEXT);
+  nsIFrame* kid = mFrames.FirstChild();
+  nsresult rv = NS_OK;
+  if (kid) {
+    // make the kid's BorderBackground our own.
+    rv = BuildDisplayListForChild(aBuilder, kid, aDirtyRect, aLists);
+  }
   UnmarkOutOfFlowChildrenForDisplayList(mFixedContainer.GetFirstChild());
   return rv;
 }