Move implementation of BrowserList onto an inner, instantiatable class, BrowserListImpl.

chrome/browser/ui/host_desktop.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_HOST_DESKTOP_H_
+#define CHROME_BROWSER_UI_HOST_DESKTOP_H_
+
+namespace chrome {
+
+// A value that specifies what desktop environment hosts a particular piece of
+// UI.
+// Note that HOST_DESKTOP_TYPE_ASH is always used on ChromeOS.
+enum HostDesktopType {
+  // The UI is hosted on the system native desktop.
+  HOST_DESKTOP_TYPE_NATIVE = 0,
+
+  // The UI is hosted in the synthetic Ash desktop.
+  HOST_DESKTOP_TYPE_ASH,
+
+  HOST_DESKTOP_TYPE_COUNT
+};
+
+/*
+TODO(beng): implement utilities as needed, e.g.:
+HostDesktopType GetActiveDesktop();
+HostDesktopType GetHostDesktopTypeForNativeView(gfx::NativeView native_view);
+HostDesktopType GetHostDesktopTypeForNativeWindow(
+    gfx::NativeWindow native_window);
+HostDesktopType GetHostDesktopTypeForBrowser(Browser* browser);
+*/
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_UI_HOST_DESKTOP_H_