Bug 1081272 - Include position and transform when computing header/footer size [r=tn]

layout/generic/nsGfxScrollFrame.cpp

@@ -3706,7 +3706,9 @@ GetScrollPortSizeExcludingHeadersAndFooters(nsIFrame* aViewportFrame,
   for (nsFrameList::Enumerator iterator(fixedFrames); !iterator.AtEnd();
        iterator.Next()) {
     nsIFrame* f = iterator.get();
-    nsRect r = f->GetRect().Intersect(aScrollPort);
+    nsRect r = f->GetRectRelativeToSelf();
+    r = nsLayoutUtils::TransformFrameRectToAncestor(f, r, aViewportFrame);
+    r = r.Intersect(aScrollPort);
     if ((r.width >= aScrollPort.width / 2 ||
          r.width >= NSIntPixelsToAppUnits(800, AppUnitsPerCSSPixel())) &&
         r.height <= aScrollPort.height/3) {

layout/generic/test/page_scroll_with_fixed_pos_window.html

@@ -91,6 +91,14 @@ function runTest() {
                  "Don't ignore elements that span more than half the viewport side");
               document.getElementById("top").style.width = "100%";
 
+              document.getElementById("top").style.top = "-40px";
+              document.getElementById("top").style.transform = "translateY(38px)";
+              scrollDownOnePageWithContinuation(function() {
+                is(document.documentElement.scrollTop,
+                   fullPageScrollDown - (10 + 13 - 40 + 38),
+                   "Account for offset and transform");
+                document.getElementById("top").style.width = "100%";
+
                 // Scroll back up so test results are visible
                 document.documentElement.scrollTop = 0;
                 SimpleTest.finish();
@@ -101,6 +109,7 @@ function runTest() {
         });
       });
     });
+  });
 }
 </script>
 </pre>