[Temp] Backport r279857 from upstream.

This is a build fix for the WebRTC disabled case.

  socket_dispatcher_host.h uses webrtc, skip when webrtc is disabled

  https://codereview.chromium.org/264793017 added some webrtc specific
  code to socket_dispatcher_host.h, and it only appears to be used for
  webrtc as far as I can see. So we should only include this file
  elsewhere when webrtc is enabled.

  BUG=363459
  TEST=build with enable_webrtc=0

  Review URL: https://codereview.chromium.org/345823003
[Temp] Backport r283541 from upstream.

This is another build fix for the WebRTC disabled case.

  content_renderer: Depend on libyuv even if WebRTC is not enabled.

  video_decoder_shim.cc uses libyuv, and the build fails if we're not
  building in component=shared_library mode and enable_webrtc=0:

  In file included from ../../third_party/libyuv/include/libyuv.h:15:0,
                   from ../../content/renderer/pepper/video_decoder_shim.cc:25:
  ../../third_party/libyuv/include/libyuv/compare.h:14:32: fatal error: libyuv/basic_types.h: No such file or directory
   #include "libyuv/basic_types.h"
                                  ^

  R=dmichael@chromium.org, bbudge@chromium.org

  Review URL: https://codereview.chromium.org/393813002