This change moves ScopedComInitializer out of core_audio_utility and into rtc_base/win so it can be reused elsewhere more easily. It also adds HSTRING and GetActivationFactory functionality to rtc_base/win. These two were heavily based on what is already present base/win. All of these are necessary for the new window capturer based on the Windows.Graphics.Capture API. You can see how these APIs will be used in this CL: 186603: Implement WgcCaptureSession | https://webrtc-review.googlesource.com/c/src/+/186603 Bug: webrtc:9273 Change-Id: I0a36373aac98be779ccbabe1053bb8d6e234f6a3 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/188523 Commit-Queue: Tommi <tommi@webrtc.org> Reviewed-by: Tommi <tommi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#32522}