[ChromeOS] Cargo cult crrev.com/556704 into VideoPlayerBrowserTest

Again, PulseAudio layer is unsupported in a target_os="chromeos" build
and VideoPlayerBrowserTest produce LOG errors about that. Again, use a
fake audio layer to eliminate it, cargo cult crrev.com/556704.

Good enough until a future CL provides a more general fix, but step #1
is to kick the VideoPlayerBrowserTest's tyres on the bots.

Bug: 835626,835742,835642
Change-Id: I58cc1c188e95d39f8e75230a761e7b69ff99cabb
Reviewed-on: https://chromium-review.googlesource.com/1049768
Reviewed-by: Stuart Langley <slangley@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557023}

chrome/browser/chromeos/file_manager/video_player_browsertest.cc

@@ -5,15 +5,22 @@
 #include "chrome/browser/chromeos/file_manager/file_manager_browsertest_base.h"
 
 #include "chromeos/chromeos_switches.h"
+#include "media/base/media_switches.h"
 
 namespace file_manager {
 
+static constexpr bool kUseFakeAudioLayer = true;
+
 template <GuestMode MODE>
 class VideoPlayerBrowserTestBase : public FileManagerBrowserTestBase {
  public:
   void SetUpCommandLine(base::CommandLine* command_line) override {
+    if (kUseFakeAudioLayer)
+      command_line->AppendSwitch(switches::kDisableAudioOutput);
+
     command_line->AppendSwitch(
         chromeos::switches::kEnableVideoPlayerChromecastSupport);
+
     FileManagerBrowserTestBase::SetUpCommandLine(command_line);
   }