[ChromeOS] AudioPlayerBrowserTest: use faked audio layer

These AudioPlayerBrowserTest run on a target_os="chromeos" linux build
which attempts to use PulseAudio for audio, and always fails [1].

The tests still PASS, since they don't need to test lower-layer audio,
but they do output PulseAudio LOG failure messages. To avoid that, use
a fake audio layer instead, which can be requested by a media command-
line switch kDisableAudioOutput after crrev.com/539638.

[1] PulseAudio won't work in this case and the LOG output of the tests
indicate that (see bug 835626 comments #3 and #7).

Bug: 835626,835742
Change-Id: I8113c15a123bfb8048141e7a20c8d02cf3341e13
Reviewed-on: https://chromium-review.googlesource.com/1047045Reviewed-by: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Naoki Fukino <fukino@chromium.org>
Reviewed-by: Max Morin <maxmorin@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556704}

chrome/browser/chromeos/file_manager/audio_player_browsertest.cc

@@ -4,11 +4,22 @@
 
 #include "chrome/browser/chromeos/file_manager/file_manager_browsertest_base.h"
 
+#include "media/base/media_switches.h"
+
 namespace file_manager {
 
+static constexpr bool kUseFakeAudioLayer = true;
+
 template <GuestMode MODE>
 class AudioPlayerBrowserTestBase : public FileManagerBrowserTestBase {
  public:
+  void SetUpCommandLine(base::CommandLine* command_line) override {
+    if (kUseFakeAudioLayer)
+      command_line->AppendSwitch(switches::kDisableAudioOutput);
+
+    FileManagerBrowserTestBase::SetUpCommandLine(command_line);
+  }
+
   GuestMode GetGuestMode() const override { return MODE; }
 
   const char* GetTestCaseName() const override {