audio_renderer_impl.cc: Only include media_switches.h on Windows.

media_switches is only used in audio_renderer_impl on Windows, so we
should only include it on Windows as well.

BUG=747229
TBR=gsennton@google.com

(cherry picked from commit ca2051b)

Change-Id: Ic4ee05430379bd31fdfd3f609111330773bc8275
Reviewed-on: https://chromium-review.googlesource.com/581196
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Anita Woodruff <awdf@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#488959}
Reviewed-on: https://chromium-review.googlesource.com/586714
Reviewed-by: Anita Woodruff <awdf@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#57}
Cr-Branched-From: ff259ba-refs/heads/master@{#488528}

Author: Anita Woodruff

media/renderers/audio_renderer_impl.cc

@@ -25,12 +25,15 @@
 #include "media/base/channel_mixing_matrix.h"
 #include "media/base/demuxer_stream.h"
 #include "media/base/media_log.h"
-#include "media/base/media_switches.h"
 #include "media/base/renderer_client.h"
 #include "media/base/timestamp_constants.h"
 #include "media/filters/audio_clock.h"
 #include "media/filters/decrypting_demuxer_stream.h"
 
+#if defined(OS_WIN)
+#include "media/base/media_switches.h"
+#endif  // defined(OS_WIN)
+
 namespace media {
 
 AudioRendererImpl::AudioRendererImpl(