Enable default media session when ChromeVox is toggled.

chrome/browser/chromeos/accessibility/accessibility_manager.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 58 matching lines @@
 #include "content/public/common/service_manager_connection.h"
 #include "extensions/browser/event_router.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/extension_messages.h"
 #include "extensions/common/extension_resource.h"
 #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"
 #include "ui/keyboard/keyboard_controller.h"
 #include "ui/keyboard/keyboard_util.h"
 
 using content::BrowserThread;
 using content::RenderViewHost;
 using extensions::api::braille_display_private::BrailleController;
 using extensions::api::braille_display_private::DisplayState;
@@ skipping 1214 matching lines @@
   }
 
   should_speak_chrome_vox_announcements_on_user_screen_ =
       chromevox_loader_->loaded_on_lock_screen();
 
   if (!chromevox_panel_) {
     chromevox_panel_ = new ChromeVoxPanel(profile_);
     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() {
   // Do any teardown work needed immediately after ChromeVox actually unloads.
   PlayEarcon(SOUND_SPOKEN_FEEDBACK_DISABLED, PlaySoundOption::ALWAYS);
   // Clear the accessibility focus ring.
   AccessibilityFocusRingController::GetInstance()->SetFocusRing(
       std::vector<gfx::Rect>(),
       AccessibilityFocusRingController::PERSIST_FOCUS_RING);
 
@@ skipping 38 matching lines @@
     content::BrowserContext* context) {
   keyboard_listener_extension_id_ = id;
 
   extensions::ExtensionRegistry* registry =
       extensions::ExtensionRegistry::Get(context);
   if (!extension_registry_observer_.IsObserving(registry) && !id.empty())
     extension_registry_observer_.Add(registry);
 }
 
 }  // namespace chromeos