Add support for loading extensions (issue #1947)

- Add CefRequestContext::LoadExtension, CefExtension, CefExtensionHandler and
  related methods/interfaces.
- Add chrome://extensions-support that lists supported Chrome APIs.
- Add CefBrowserHost::SetAutoResizeEnabled and CefDisplayHandler::OnAutoResize
  to support browser resize based on preferred web contents size.
- views: Add support for custom CefMenuButton popups.
- cefclient: Run with `--load-extension=set_page_color` command-line flag for
  an extension loading example. Add `--use-views` on Windows and Linux for an
  even better example.

libcef_dll/ctocpp/views/menu_button_pressed_lock_ctocpp.cc

@@ -0,0 +1,45 @@
+// Copyright (c) 2017 The Chromium Embedded Framework Authors. All rights
+// reserved. Use of this source code is governed by a BSD-style license that
+// can be found in the LICENSE file.
+//
+// ---------------------------------------------------------------------------
+//
+// This file was generated by the CEF translator tool. If making changes by
+// hand only do so within the body of existing method and function
+// implementations. See the translator.README.txt file in the tools directory
+// for more information.
+//
+// $hash=c43f3b09cdeca57178d011390a0b1aef581ead6a$
+//
+
+#include "libcef_dll/ctocpp/views/menu_button_pressed_lock_ctocpp.h"
+
+// CONSTRUCTOR - Do not edit by hand.
+
+CefMenuButtonPressedLockCToCpp::CefMenuButtonPressedLockCToCpp() {}
+
+template <>
+cef_menu_button_pressed_lock_t* CefCToCppRefCounted<
+    CefMenuButtonPressedLockCToCpp,
+    CefMenuButtonPressedLock,
+    cef_menu_button_pressed_lock_t>::UnwrapDerived(CefWrapperType type,
+                                                   CefMenuButtonPressedLock*
+                                                       c) {
+  NOTREACHED() << "Unexpected class type: " << type;
+  return NULL;
+}
+
+#if DCHECK_IS_ON()
+template <>
+base::AtomicRefCount CefCToCppRefCounted<
+    CefMenuButtonPressedLockCToCpp,
+    CefMenuButtonPressedLock,
+    cef_menu_button_pressed_lock_t>::DebugObjCt ATOMIC_DECLARATION;
+#endif
+
+template <>
+CefWrapperType
+    CefCToCppRefCounted<CefMenuButtonPressedLockCToCpp,
+                        CefMenuButtonPressedLock,
+                        cef_menu_button_pressed_lock_t>::kWrapperType =
+        WT_MENU_BUTTON_PRESSED_LOCK;