chromeos: Move ownership of system tray width from chrome to ash

ash/common/system/tray/default_system_tray_delegate.cc

Index: ash/common/system/tray/default_system_tray_delegate.cc
diff --git a/ash/common/system/tray/default_system_tray_delegate.cc b/ash/common/system/tray/default_system_tray_delegate.cc
index f58c2141d32010c7b2ff868b3197a748d29cba2e..ffd81256772b517f0361725b51b86176e35b2d21 100644
--- a/ash/common/system/tray/default_system_tray_delegate.cc
+++ b/ash/common/system/tray/default_system_tray_delegate.cc
@@ -63,9 +63,4 @@ bool DefaultSystemTrayDelegate::GetBluetoothDiscovering() {
   return false;
 }
 
-int DefaultSystemTrayDelegate::GetSystemTrayMenuWidth() {
-  // This is the default width for English languages.
-  return 300;
-}
-
 }  // namespace ash