mash: Migrate ash/system/user to ash/common.

ash/ash.gyp

Index: ash/ash.gyp
diff --git a/ash/ash.gyp b/ash/ash.gyp
index e28f3d7e994a797240a9d60f573218d3f69ab43e..d2dce7d8e1515fc0bafbb6fdde1620497897c942 100644
--- a/ash/ash.gyp
+++ b/ash/ash.gyp
@@ -283,9 +283,15 @@
       'common/system/user/login_status.h',
       'common/system/user/rounded_image_view.cc',
       'common/system/user/rounded_image_view.h',
+      'common/system/user/tray_user.cc',
+      'common/system/user/tray_user.h',
       'common/system/user/tray_user_separator.cc',
       'common/system/user/tray_user_separator.h',
+      'common/system/user/user_card_view.cc',
+      'common/system/user/user_card_view.h',
       'common/system/user/user_observer.h',
+      'common/system/user/user_view.cc',
+      'common/system/user/user_view.h',
       'common/system/volume_control_delegate.h',
       'common/system/web_notification/ash_popup_alignment_delegate.cc',
       'common/system/web_notification/ash_popup_alignment_delegate.h',
@@ -636,12 +642,6 @@
       'system/toast/toast_overlay.h',
       'system/tray/system_tray.cc',
       'system/tray/system_tray.h',
-      'system/user/tray_user.cc',
-      'system/user/tray_user.h',
-      'system/user/user_card_view.cc',
-      'system/user/user_card_view.h',
-      'system/user/user_view.cc',
-      'system/user/user_view.h',
       'touch/touch_hud_debug.cc',
       'touch/touch_hud_debug.h',
       'touch/touch_hud_projection.cc',
@@ -910,6 +910,7 @@
       'common/system/ime/tray_ime_chromeos_unittest.cc',
       'common/system/tray/tray_details_view_unittest.cc',
       'common/system/update/tray_update_unittest.cc',
+      'common/system/user/tray_user_unittest.cc',
       'content/display/screen_orientation_controller_chromeos_unittest.cc',
       'content/keyboard_overlay/keyboard_overlay_delegate_unittest.cc',
       'content/keyboard_overlay/keyboard_overlay_view_unittest.cc',
@@ -971,7 +972,6 @@
       'system/overview/overview_button_tray_unittest.cc',
       'system/toast/toast_manager_unittest.cc',
       'system/tray/system_tray_unittest.cc',
-      'system/user/tray_user_unittest.cc',
       'system/web_notification/ash_popup_alignment_delegate_unittest.cc',
       'system/web_notification/web_notification_tray_unittest.cc',
       'test/ash_test_helper_unittest.cc',