cros: Suspend media sessions with display off trigger by tablet power button

chrome/browser/ui/ash/chrome_shell_delegate.cc

 // Copyright (c) 2012 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/ui/ash/chrome_shell_delegate.h"
 
 #include <stddef.h>
 
 #include <limits>
 
@@ skipping 42 matching lines @@
 #include "chrome/browser/ui/ash/system_tray_delegate_chromeos.h"
 #include "chrome/browser/ui/aura/accessibility/automation_manager_aura.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_commands.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_navigator.h"
 #include "chrome/browser/ui/browser_navigator_params.h"
 #include "chrome/browser/ui/browser_tabstrip.h"
 #include "chrome/browser/ui/browser_window.h"
 #include "chrome/browser/ui/scoped_tabbed_browser_displayer.h"
+#include "chrome/browser/ui/tab_contents/tab_contents_iterator.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/grit/chromium_strings.h"
 #include "chrome/grit/generated_resources.h"
 #include "chrome/grit/theme_resources.h"
 #include "chromeos/chromeos_switches.h"
 #include "components/prefs/pref_service.h"
 #include "components/user_manager/user.h"
 #include "components/user_manager/user_manager.h"
+#include "content/public/browser/media_session.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/common/service_manager_connection.h"
+#include "media/base/media_switches.h"
 #include "ui/aura/window.h"
 #include "ui/base/ime/chromeos/input_method_manager.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 
 using chromeos::AccessibilityManager;
 
 namespace {
 
 const char kKeyboardShortcutHelpPageUrl[] =
@@ skipping 373 matching lines @@
 
   bool first_run_after_boot = base::CommandLine::ForCurrentProcess()->HasSwitch(
       chromeos::switches::kFirstExecAfterBoot);
   chromeos::LoadDisplayPreferences(first_run_after_boot);
   // Object owns itself, and deletes itself when Observer::OnShutdown is called:
   new policy::DisplayRotationDefaultHandler();
   // Set the observer now so that we can save the initial state
   // in Shell::Init.
   display_configuration_observer_.reset(
       new chromeos::DisplayConfigurationObserver());
+
+  // Append switch for SuspendMediaSessions() that will suspend media players
+  // without turning on audio focus.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      ::switches::kEnableInternalMediaSession);

[Daniel Erat, 2017/05/22 23:38:34]

src/content/browser/media/session/media_session_controllers_manager.cc currently
contains the following:

bool IsMediaSessionEnabled() {
#if defined(OS_ANDROID)
  return true;
#else
  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
  return command_line->HasSwitch(switches::kEnableInternalMediaSession) ||
         command_line->HasSwitch(switches::kEnableAudioFocus);
#endif
}

i think it'd be cleaner to change the condition to also check
defined(OS_CHROMEOS), probably along with a comment explaining why this is
needed on chrome os.

that's assuming that the media session owners agree, though. :-)

[Qiang(Joe) Xu, 2017/05/23 17:54:46]

Done. mlamouri@, do you agree on this?

 }
 
 void ChromeShellDelegate::PreShutdown() {
   display_configuration_observer_.reset();
 }
 
 void ChromeShellDelegate::Exit() {
   chrome::AttemptUserExit();
 }
 
@@ skipping 107 matching lines @@
 
 void ChromeShellDelegate::UpdateTouchscreenStatusFromPrefs() {
   chromeos::system::InputDeviceSettings::Get()
       ->UpdateTouchscreenStatusFromPrefs();
 }
 
 void ChromeShellDelegate::ToggleTouchpad() {
   chromeos::system::InputDeviceSettings::Get()->ToggleTouchpad();
 }
 
+void ChromeShellDelegate::SuspendMediaSessions() {
+  for (TabContentsIterator it; !it.done(); it.Next()) {
+    content::MediaSession::Get(*it)->Suspend(
+        content::MediaSession::SuspendType::SYSTEM);
+  }
+}
+
 keyboard::KeyboardUI* ChromeShellDelegate::CreateKeyboardUI() {
   return new ChromeKeyboardUI(ProfileManager::GetActiveUserProfile());
 }
 
 ash::SessionStateDelegate* ChromeShellDelegate::CreateSessionStateDelegate() {
   return new SessionStateDelegateChromeos;
 }
 
 ash::AccessibilityDelegate* ChromeShellDelegate::CreateAccessibilityDelegate() {
   return new AccessibilityDelegateImpl;
@@ skipping 42 matching lines @@
       NOTREACHED() << "Unexpected notification " << type;
   }
 }
 
 void ChromeShellDelegate::PlatformInit() {
   registrar_.Add(this, chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED,
                  content::NotificationService::AllSources());
   registrar_.Add(this, chrome::NOTIFICATION_SESSION_STARTED,
                  content::NotificationService::AllSources());
 }