Fix 64-bit use of Win32Window. An incorrect call to SetWindowLongPtr was crashing the 64-bit test. BUG=angle:705 Change-Id: I3815bb0a1308f5e66e74faead37c0ae09f975a10 Reviewed-on: https://chromium-review.googlesource.com/214883 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>