Bug 1324591 - Add nsLayoutUtils::IsInPositionFixedSubtree. r=TYLin

Depends on D75729

Differential Revision: https://phabricator.services.mozilla.com/D81480

dom/base/nsDOMWindowUtils.cpp

@@ -2615,13 +2615,9 @@ nsDOMWindowUtils::ZoomToFocusedInput() {
     // Note that we only do this if the frame belongs to `presShell` (that is,
     // we still zoom in fixed elements in subdocuments, as they're not fixed to
     // the root content document).
-    if (frame->PresShell() == presShell) {
-      for (; frame; frame = frame->GetParent()) {
-        if (frame->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
-            nsLayoutUtils::IsReallyFixedPos(frame)) {
-          return true;
-        }
-      }
+    if (frame->PresShell() == presShell &&
+        nsLayoutUtils::IsInPositionFixedSubtree(frame)) {
+      return true;
     }
     return false;
   }();

layout/base/AccessibleCaret.cpp

@@ -174,14 +174,8 @@ void AccessibleCaret::EnsureApzAware() {
 }
 
 bool AccessibleCaret::IsInPositionFixedSubtree() const {
-  for (nsIFrame* f = mImaginaryCaretReferenceFrame.GetFrame(); f;
-       f = f->GetParent()) {
-    if (f->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
-        nsLayoutUtils::IsReallyFixedPos(f)) {
-      return true;
-    }
-  }
-  return false;
+  return nsLayoutUtils::IsInPositionFixedSubtree(
+      mImaginaryCaretReferenceFrame.GetFrame());
 }
 
 void AccessibleCaret::InjectCaretElement(Document* aDocument) {

layout/base/nsLayoutUtils.cpp

@@ -7653,6 +7653,17 @@ bool nsLayoutUtils::MayBeReallyFixedPos(const nsIFrame* aFrame) {
          parentType == LayoutFrameType::PageContent;
 }
 
+/* static */
+bool nsLayoutUtils::IsInPositionFixedSubtree(const nsIFrame* aFrame) {
+  for (const nsIFrame* f = aFrame; f; f = f->GetParent()) {
+    if (f->StyleDisplay()->mPosition == StylePositionProperty::Fixed &&
+        nsLayoutUtils::IsReallyFixedPos(f)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 nsLayoutUtils::SurfaceFromElementResult
 nsLayoutUtils::SurfaceFromOffscreenCanvas(OffscreenCanvas* aOffscreenCanvas,
                                           uint32_t aSurfaceFlags,

layout/base/nsLayoutUtils.h

@@ -2186,6 +2186,11 @@ class nsLayoutUtils {
    */
   static bool MayBeReallyFixedPos(const nsIFrame* aFrame);
 
+  /**
+   * Returns true if |aFrame| is inside position:fixed subtree.
+   */
+  static bool IsInPositionFixedSubtree(const nsIFrame* aFrame);
+
   /**
    * Obtain a SourceSurface from the given DOM element, if possible.
    * This obtains the most natural surface from the element; that