Use fake audio streams in browser tests on Linux.

Due to problems with PulseAudio failing to start, tests
using audio are flaking. Using fake audio prevents the
flakes.

Bug: 986021
Change-Id: I17d622637126ad003f5c3f63aaa5559db4bc20b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2096768
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749299}

content/browser/back_forward_cache_browsertest.cc

@@ -112,6 +112,12 @@ class BackForwardCacheBrowserTest : public ContentBrowserTest,
         switches::kIgnoreCertificateErrors);
     base::CommandLine::ForCurrentProcess()->AppendSwitch(
         switches::kEnableExperimentalWebPlatformFeatures);
+#if defined(OS_LINUX)
+    // Due to problems with PulseAudio failing to start, use a fake audio
+    // stream. https://crbug.com/1047655#c70
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(
+        switches::kDisableAudioOutput);
+#endif
     // TODO(sreejakshetty): Initialize ScopedFeatureLists from test constructor.
     EnableFeatureAndSetParams(features::kBackForwardCache,
                               "TimeToLiveInBackForwardCacheInSeconds", "3600");

content/browser/renderer_host/render_process_host_browsertest.cc

@@ -917,6 +917,11 @@ class CaptureStreamRenderProcessHostTest : public RenderProcessHostTest {
   }
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
+#if defined(OS_LINUX)
+    // Due to problems with PulseAudio failing to start, use a fake audio
+    // stream. https://crbug.com/1047655#c70
+    command_line->AppendSwitch(switches::kDisableAudioOutput);
+#endif
     // These flags are necessary to emulate camera input for getUserMedia()
     // tests.
     command_line->AppendSwitch(switches::kUseFakeUIForMediaStream);