Bug 1523500 - Don't use cross-doc checks for perspective scrolling. r=mattwoodrow

Would be pretty surprising if a perspective transform scrolled stuff in an
iframe for example.

Differential Revision: https://phabricator.services.mozilla.com/D17905

--HG--
extra : moz-landing-system : lando

layout/base/nsLayoutUtils.cpp

@@ -1489,15 +1489,23 @@ bool nsLayoutUtils::IsAncestorFrameCrossDoc(const nsIFrame* aAncestorFrame,
   return aCommonAncestor == aAncestorFrame;
 }
 
+bool nsLayoutUtils::IsAncestorFrame(const nsIFrame* aAncestorFrame,
+                                    const nsIFrame* aFrame,
+                                    const nsIFrame* aCommonAncestor) {
+  for (const nsIFrame* f = aFrame; f != aCommonAncestor; f = f->GetParent()) {
+    if (f == aAncestorFrame) {
+      return true;
+    }
+  }
+  return aCommonAncestor == aAncestorFrame;
+}
+
 // static
 bool nsLayoutUtils::IsProperAncestorFrame(const nsIFrame* aAncestorFrame,
                                           const nsIFrame* aFrame,
                                           const nsIFrame* aCommonAncestor) {
-  if (aFrame == aAncestorFrame) return false;
-  for (const nsIFrame* f = aFrame; f != aCommonAncestor; f = f->GetParent()) {
-    if (f == aAncestorFrame) return true;
-  }
-  return aCommonAncestor == aAncestorFrame;
+  return aFrame != aAncestorFrame &&
+    IsAncestorFrame(aAncestorFrame, aFrame, aCommonAncestor);
 }
 
 // static

layout/base/nsLayoutUtils.h

@@ -532,6 +532,17 @@ class nsLayoutUtils {
                                     const nsIFrame* aFrame,
                                     const nsIFrame* aCommonAncestor = nullptr);
 
+  /**
+   * IsAncestorFrame checks whether aAncestorFrame is an ancestor
+   * of aFrame or equal to aFrame.
+   * @param aCommonAncestor nullptr, or a common ancestor of aFrame and
+   * aAncestorFrame. If non-null, this can bound the search and speed up
+   * the function
+   */
+  static bool IsAncestorFrame(const nsIFrame* aAncestorFrame,
+                              const nsIFrame* aFrame,
+                              const nsIFrame* aCommonAncestor = nullptr);
+
   /**
    * Like IsProperAncestorFrame, but looks across document boundaries.
    *

layout/painting/FrameLayerBuilder.cpp

@@ -4267,8 +4267,7 @@ static const ActiveScrolledRoot* GetASRForPerspective(
     const ActiveScrolledRoot* aASR, nsIFrame* aPerspectiveFrame) {
   for (const ActiveScrolledRoot* asr = aASR; asr; asr = asr->mParent) {
     nsIFrame* scrolledFrame = asr->mScrollableFrame->GetScrolledFrame();
-    if (nsLayoutUtils::IsAncestorFrameCrossDoc(scrolledFrame,
-                                               aPerspectiveFrame)) {
+    if (nsLayoutUtils::IsAncestorFrame(scrolledFrame, aPerspectiveFrame)) {
       return asr;
     }
   }

layout/painting/nsDisplayList.cpp

@@ -8500,7 +8500,7 @@ bool nsDisplayPerspective::CreateWebRenderCommands(
 
   Maybe<uint64_t> scrollingRelativeTo;
   for (auto* asr = GetActiveScrolledRoot(); asr; asr = asr->mParent) {
-    if (nsLayoutUtils::IsAncestorFrameCrossDoc(
+    if (nsLayoutUtils::IsAncestorFrame(
           asr->mScrollableFrame->GetScrolledFrame(), perspectiveFrame)) {
       scrollingRelativeTo.emplace(asr->GetViewId());
       break;