Don't try to initialize PulseAudio if audio output disabled

Due to problems on some bots failing to start PulseAudio and causing
Chrome startup to hang, avoid trying to initialize PulseAudio if audio
output has been disabled.

Bug: 986021,1023029,1026849,1035472,1049467
Test: media content_browsertests pass
Change-Id: Ib75e44843df6e9e54d85ee4bd164b091ab2ade70
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062694
Commit-Queue: John Rummell <jrummell@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742251}

media/audio/linux/audio_manager_linux.cc

@@ -6,12 +6,11 @@
 
 #include "base/command_line.h"
 #include "base/metrics/histogram_macros.h"
+#include "media/audio/fake_audio_manager.h"
 #include "media/base/media_switches.h"
 
 #if defined(USE_ALSA)
 #include "media/audio/alsa/audio_manager_alsa.h"
-#else
-#include "media/audio/fake_audio_manager.h"
 #endif
 #if defined(USE_CRAS)
 #include "media/audio/cras/audio_manager_cras.h"
@@ -33,6 +32,13 @@ enum LinuxAudioIO {
 std::unique_ptr<media::AudioManager> CreateAudioManager(
     std::unique_ptr<AudioThread> audio_thread,
     AudioLogFactory* audio_log_factory) {
+  // For testing allow audio output to be disabled.
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDisableAudioOutput)) {
+    return std::make_unique<FakeAudioManager>(std::move(audio_thread),
+                                              audio_log_factory);
+  }
+
 #if defined(USE_CRAS)
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kUseCras)) {
     UMA_HISTOGRAM_ENUMERATION("Media.LinuxAudioIO", kCras, kAudioIOMax + 1);