Create an api for easily converting between the coordinate systems of two

frames or two views.  Use this to fix the auto-positioning of abs pos boxes to
work no matter how their containing block and the block their placeholder lives
in are related, and convert various other callers to the new API.  Bug 266968,
r+sr=roc


git-svn-id: svn://10.0.0.236/trunk@164857 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/layout/base/nsCSSRendering.cpp

@@ -3015,18 +3015,11 @@ nsCSSRendering::PaintBackgroundWithSC(nsPresContext* aPresContext,
     ComputeBackgroundAnchorPoint(aColor, viewportArea, viewportArea, tileWidth, tileHeight, anchor);
 
     // Convert the anchor point to aForFrame's coordinate space
-    nsIView* view = aForFrame->GetView();
-    if (!view) {
-      nsPoint offset;
-      aForFrame->GetOffsetFromView(aPresContext, offset, &view);
-      anchor -= offset;
-    }
+    nsPoint offset(0, 0);
+    nsIView* view = aForFrame->GetClosestView(&offset);
+    anchor -= offset;
     NS_ASSERTION(view, "expected a view");
-    while (view && (view != viewportView)) {
-      anchor -= view->GetPosition();
-      // Get the parent view until we reach the viewport view
-      view = view->GetParent();
-    }
+    anchor -= view->GetOffsetTo(viewportView);
   } else {
     if (frameType == nsLayoutAtoms::canvasFrame) {
       // If the frame is the canvas, the image is placed relative to