1 files changed, 64 insertions, 0 deletions
diff --git a/layout/base/DepthOrderedFrameList.h b/layout/base/DepthOrderedFrameList.h
new file mode 100644
index 0000000000..a12a5c9c86
--- /dev/null
+++ b/layout/base/DepthOrderedFrameList.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_DepthOrderedFrameList_h
+#define mozilla_DepthOrderedFrameList_h
+
+#include "mozilla/ReverseIterator.h"
+#include "nsTArray.h"
+
+class nsIFrame;
+
+namespace mozilla {
+
+class DepthOrderedFrameList {
+ public:
+  // Add a dirty root.
+  void Add(nsIFrame* aFrame);
+  // Remove this frame if present.
+  void Remove(nsIFrame* aFrame);
+  // Remove and return one of the shallowest dirty roots from the list.
+  // (If two roots are at the same depth, order is indeterminate.)
+  nsIFrame* PopShallowestRoot();
+  // Remove all dirty roots.
+  void Clear() { mList.Clear(); }
+  // Is this frame one of the elements in the list?
+  bool Contains(nsIFrame* aFrame) const { return mList.Contains(aFrame); }
+  // Are there no elements?
+  bool IsEmpty() const { return mList.IsEmpty(); }
+
+  // Is the given frame an ancestor of any dirty root?
+  bool FrameIsAncestorOfAnyElement(nsIFrame* aFrame) const;
+
+  auto IterFromShallowest() const { return Reversed(mList); }
+
+ private:
+  struct FrameAndDepth {
+    nsIFrame* mFrame;
+    const uint32_t mDepth;
+
+    // Easy conversion to nsIFrame*, as it's the most likely need.
+    operator nsIFrame*() const { return mFrame; }
+
+    // Used to sort by reverse depths, i.e., deeper < shallower.
+    class CompareByReverseDepth {
+     public:
+      bool Equals(const FrameAndDepth& aA, const FrameAndDepth& aB) const {
+        return aA.mDepth == aB.mDepth;
+      }
+      bool LessThan(const FrameAndDepth& aA, const FrameAndDepth& aB) const {
+        // Reverse depth! So '>' instead of '<'.
+        return aA.mDepth > aB.mDepth;
+      }
+    };
+  };
+  // List of all known dirty roots, sorted by decreasing depths.
+  nsTArray<FrameAndDepth> mList;
+};
+
+}  // namespace mozilla
+
+#endif