Windows: refactor `WindowEnumerator` into `base::win`

This is to allow reuse of the `WindowEnumerator` functionality.

Fixed: 1482637
Change-Id: I880f3232982cf795f9ae3f8f7a0e01ddfff450be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4865654
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Xiaoling Bao <xiaolingbao@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Auto-Submit: S Ganesh <ganesh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1196770}

diff --git a/base/win/window_enumerator.h b/base/win/window_enumerator.h
new file mode 100644
index 0000000..ee68ce40
--- /dev/null
+++ b/base/win/window_enumerator.h

@@ -0,0 +1,59 @@
+// Copyright 2023 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_WIN_WINDOW_ENUMERATOR_H_
+#define BASE_WIN_WINDOW_ENUMERATOR_H_
+
+#include <windows.h>
+
+#include <string>
+
+#include "base/base_export.h"
+#include "base/functional/callback.h"
+
+namespace base::win {
+
+// Enumerates immediate child windows of `parent`, and calls `filter.Run` for
+// each window:
+// * If `filter.Run` returns `false`, continues enumerating.
+// * If `filter.Run` returns `true`, stops enumerating.
+class BASE_EXPORT WindowEnumerator {
+ public:
+  WindowEnumerator(HWND parent,
+                   base::RepeatingCallback<bool(HWND hwnd)> filter);
+  WindowEnumerator(const WindowEnumerator&) = delete;
+  WindowEnumerator& operator=(const WindowEnumerator&) = delete;
+  ~WindowEnumerator();
+
+  void Run() const;
+
+  // Returns true if `hwnd` is an always-on-top window.
+  static bool IsTopmostWindow(HWND hwnd);
+
+  // Returns true if `hwnd` is a system dialog.
+  static bool IsSystemDialog(HWND hwnd);
+
+  // Returns true if `hwnd` is a window owned by the Windows shell.
+  static bool IsShellWindow(HWND hwnd);
+
+  // Returns the class name of `hwnd` or an empty string on error.
+  static std::wstring GetWindowClass(HWND hwnd);
+
+  // Returns the window text for `hwnd`, or an empty string on error.
+  static std::wstring GetWindowText(HWND hwnd);
+
+ private:
+  // Main processing function run for each window.
+  bool OnWindow(HWND hwnd) const;
+
+  // An EnumWindowsProc invoked by EnumWindows once for each window.
+  static BOOL CALLBACK OnWindowProc(HWND hwnd, LPARAM lparam);
+
+  const HWND parent_;
+  base::RepeatingCallback<bool(HWND hwnd)> filter_;
+};
+
+}  // namespace base::win
+
+#endif  // BASE_WIN_WINDOW_ENUMERATOR_H_