Address Win/Clang style plugin error in hwnd_message_handler.h
Address Win/Clang style plugin error in hwnd_message_handler.h

This should fix the error below, and also make the code adhere to the comment
in the header: "The WeakPtrFactories below must occur last" :-)

In file included from ..\..\ui\views\win\hwnd_message_handler.cc:5:
..\..\ui/views/win/hwnd_message_handler.h(594,44) :  error: [chromium-style]
WeakPtrFactory members which refer to their outer class must be the last member
in the outer class definition.
  base::WeakPtrFactory<HWNDMessageHandler> autohide_factory_;
                                           ^

BUG=82385
TBR=sky

Review URL: https://codereview.chromium.org/1286273002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#343096}

ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend