Add VideoDecoderProxy to RenderProcessHost registry.

This path is similar to MediaInterfaceProxy registered in
RenderFrameHost, except that VideoDecoderProxy only supports creating
video decoders. This will enable WebRTC's RTCVideoDecoderFactory to
create hardware video decoders using MojoVideoDecoder.

Bug: 857111
Change-Id: If960000688e636ade49d749bc99e9217f784e853
Reviewed-on: https://chromium-review.googlesource.com/1117214
Reviewed-by: Ken Buchanan <[email protected]>
Reviewed-by: Xiaohan Wang <[email protected]>
Commit-Queue: Dan Sanders <[email protected]>
Cr-Commit-Position: refs/heads/master@{#582779}
diff --git a/content/browser/BUILD.gn b/content/browser/BUILD.gn
index c9bb570..9cb8d99 100644
--- a/content/browser/BUILD.gn
+++ b/content/browser/BUILD.gn
@@ -1161,6 +1161,8 @@
     "media/session/media_session_uma_helper.h",
     "media/url_provision_fetcher.cc",
     "media/url_provision_fetcher.h",
+    "media/video_decoder_proxy.cc",
+    "media/video_decoder_proxy.h",
     "memory/memory_condition_observer.cc",
     "memory/memory_condition_observer.h",
     "memory/memory_coordinator_default_policy.cc",