Enable default media session when ChromeVox is toggled.

chrome/browser/chromeos/accessibility/accessibility_manager.cc

Index: chrome/browser/chromeos/accessibility/accessibility_manager.cc
diff --git a/chrome/browser/chromeos/accessibility/accessibility_manager.cc b/chrome/browser/chromeos/accessibility/accessibility_manager.cc
index 744d724485a505756031c6051a4ed8cf0d0698d8..9fbb2731130982565528c13c41e26c18c14231b2 100644
--- a/chrome/browser/chromeos/accessibility/accessibility_manager.cc
+++ b/chrome/browser/chromeos/accessibility/accessibility_manager.cc
@@ -76,6 +76,7 @@
 #include "extensions/common/host_id.h"
 #include "mash/public/interfaces/launchable.mojom.h"
 #include "media/audio/sounds/sounds_manager.h"
+#include "media/base/media_switches.h"
 #include "services/service_manager/public/cpp/connector.h"
 #include "ui/base/ime/chromeos/input_method_manager.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -1310,6 +1311,9 @@ void AccessibilityManager::PostLoadChromeVox() {
     chromevox_panel_widget_observer_.reset(
         new ChromeVoxPanelWidgetObserver(chromevox_panel_->GetWidget(), this));
   }
+
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(

[dmazzoni, 2016/12/15 18:27:42]

Add a guard to do this only if the flag isn't already set, for two reasons:
1. Don't want to keep appending it when toggling, and
2. The flag may have already been set to kEnableDefaultMediaSessionDuckFlash
and you don't want to disable that

+      switches::kEnableDefaultMediaSession);
 }
 
 void AccessibilityManager::PostUnloadChromeVox() {