mash: Move SystemTrayImage and TrayImageItem to //ash/common

ash/ash.gyp

Index: ash/ash.gyp
diff --git a/ash/ash.gyp b/ash/ash.gyp
index 43c6829efb98d30609d05d78eb5200c2988b8795..c2b11788bd3945231fdc22d83562da0877a784b0 100644
--- a/ash/ash.gyp
+++ b/ash/ash.gyp
@@ -101,8 +101,16 @@
       'common/system/tray/fixed_sized_image_view.h',
       'common/system/tray/system_tray_delegate.cc',
       'common/system/tray/system_tray_delegate.h',
+      'common/system/tray/system_tray_item.cc',
+      'common/system/tray/system_tray_item.h',
       'common/system/tray/tray_constants.cc',
       'common/system/tray/tray_constants.h',
+      'common/system/tray/tray_image_item.cc',
+      'common/system/tray/tray_image_item.h',
+      'common/system/tray/tray_item_view.cc',
+      'common/system/tray/tray_item_view.h',
+      'common/system/tray/tray_utils.cc',
+      'common/system/tray/tray_utils.h',
       'common/system/tray/wm_system_tray_notifier.cc',
       'common/system/tray/wm_system_tray_notifier.h',
       'common/system/update/update_observer.h',
@@ -561,8 +569,6 @@
       'system/tray/system_tray.h',
       'system/tray/system_tray_bubble.cc',
       'system/tray/system_tray_bubble.h',
-      'system/tray/system_tray_item.cc',
-      'system/tray/system_tray_item.h',
       'system/tray/system_tray_notifier.cc',
       'system/tray/system_tray_notifier.h',
       'system/tray/throbber_view.cc',
@@ -579,12 +585,8 @@
       'system/tray/tray_empty.h',
       'system/tray/tray_event_filter.cc',
       'system/tray/tray_event_filter.h',
-      'system/tray/tray_image_item.cc',
-      'system/tray/tray_image_item.h',
       'system/tray/tray_item_more.cc',
       'system/tray/tray_item_more.h',
-      'system/tray/tray_item_view.cc',
-      'system/tray/tray_item_view.h',
       'system/tray/tray_notification_view.cc',
       'system/tray/tray_notification_view.h',
       'system/tray/tray_popup_header_button.cc',
@@ -595,8 +597,6 @@
       'system/tray/tray_popup_label_button.h',
       'system/tray/tray_popup_label_button_border.cc',
       'system/tray/tray_popup_label_button_border.h',
-      'system/tray/tray_utils.cc',
-      'system/tray/tray_utils.h',
       'system/tray/view_click_listener.h',
       'system/tray_accessibility.cc',
       'system/tray_accessibility.h',