Fix Win32Window::takeScreenshot. Several parts of this function were incorrectly checking for errors or passing the wrong parameters. If screenshotting fails, throw an exception in dEQP so that it is converted to a test failure instead of hanging the test. BUG=angleproject:2075 Change-Id: I19b55b273d0d3f1b47c1dac6affca69de8db21e0 Reviewed-on: https://chromium-review.googlesource.com/587300 Commit-Queue: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>