1 files changed, 54 insertions, 0 deletions
diff --git a/layout/generic/AnonymousContentKey.h b/layout/generic/AnonymousContentKey.h
new file mode 100644
index 0000000000..531754fd20
--- /dev/null
+++ b/layout/generic/AnonymousContentKey.h
@@ -0,0 +1,54 @@
+/* -*- 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/. */
+
+/* values to identify particular subtrees of native anonymous content */
+
+#ifndef mozilla_AnonymousContentKey_h
+#define mozilla_AnonymousContentKey_h
+
+#include "mozilla/TypedEnumBits.h"
+#include <stdint.h>
+#include "X11UndefineNone.h"
+
+namespace mozilla {
+
+// clang-format off
+
+// We currently use cached anonymous content styles only for scrollbar parts,
+// and we can fit the type of scrollbar part element along with its different
+// options (such as orientation, and other attribute values that can affect
+// styling) into a uint8_t.
+//
+// The lower three bits hold a Type_* value identifying the type of
+// element, and the remaining bits store Flag_* values.
+//
+// A value of 0 is used to represent an anonymous content subtree that we don't
+// cache styles for.
+enum class AnonymousContentKey : uint8_t {
+  None                           = 0x00,
+
+  // all
+  Type_ScrollCorner              = 0x01,
+  Type_Scrollbar                 = 0x02,
+  Type_ScrollbarButton           = 0x03,
+  Type_Slider                    = 0x04,
+
+  // scrollbar, scrollbarbutton, slider
+  Flag_Vertical                  = 0x08,
+
+  // scrollbarbutton
+  Flag_ScrollbarButton_Down      = 0x10,
+  Flag_ScrollbarButton_Bottom    = 0x20,
+  Flag_ScrollbarButton_Decrement = 0x40,
+};
+
+// clang-format on
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(AnonymousContentKey)
+
+}  // namespace mozilla
+
+#endif  // mozilla_AnonymousContentKey_h