Bug 1229853 - Don't apply the displayport multiplier if we don't have a frame for the element the displayport is set on. r=tn

layout/base/nsLayoutUtils.cpp

@@ -890,10 +890,11 @@ GetDisplayPortFromMarginsData(nsIContent* aContent,
   nsIFrame* frame = aContent->GetPrimaryFrame();
   if (!frame) {
     // Turns out we can't really compute it. Oops. We still should return
-    // something sane. Note that although we can apply the multiplier on the
+    // something sane. Note that since we can't clamp the rect without a
-    // base rect here, we can't tile-align or clamp the rect without a frame.
+    // frame, we don't apply the multiplier either as it can cause the result
+    // to leak outside the scrollable area.
     NS_WARNING("Attempting to get a displayport from a content with no primary frame!");
-    return ApplyRectMultiplier(base, aMultiplier);
+    return base;
   }
 
   bool isRoot = false;
@@ -903,7 +904,7 @@ GetDisplayPortFromMarginsData(nsIContent* aContent,
     frame = frame->PresContext()->PresShell()->GetRootScrollFrame();
     if (!frame) {
       // If there is no root scrollframe, just exit.
-      return ApplyRectMultiplier(base, aMultiplier);
+      return base;
     }
 
     isRoot = true;