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

ash/system/power/tablet_power_button_controller.cc

Index: ash/system/power/tablet_power_button_controller.cc
diff --git a/ash/system/power/tablet_power_button_controller.cc b/ash/system/power/tablet_power_button_controller.cc
index 7d2fcc9c4b4e449120462abd010cf47885aab433..314eb01eb8fc86bc4b2c01a24dbf64cf0ff2f4fa 100644
--- a/ash/system/power/tablet_power_button_controller.cc
+++ b/ash/system/power/tablet_power_button_controller.cc
@@ -222,6 +222,11 @@ void TabletPowerButtonController::SetDisplayForcedOff(bool forced_off) {
   backlights_forced_off_ = forced_off;
   UpdateTouchscreenStatus();
 
+  if (backlights_forced_off_) {
+    ShellDelegate* delegate = Shell::Get()->shell_delegate();
+    delegate->SuspendMediaSessions();

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

nit: i'd put this on a single line since you only use the delegate once:

  Shell::Get()->shell_delegate()->SuspendMediaSessions();

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

Done.

+  }
+
   // Send an a11y alert.
   Shell::Get()->accessibility_delegate()->TriggerAccessibilityAlert(
       forced_off ? A11Y_ALERT_SCREEN_OFF : A11Y_ALERT_SCREEN_ON);