Log device/usb messages to chrome://device-log.

chromeos/device_event_log.h

Index: chromeos/device_event_log.h
diff --git a/chromeos/device_event_log.h b/chromeos/device_event_log.h
index a71f8d6d7e81b88bc08e2a6c2210e3b2159e4964..22b6a5112d798536f16d6cd74904db5c2797d48e 100644
--- a/chromeos/device_event_log.h
+++ b/chromeos/device_event_log.h
@@ -33,6 +33,9 @@ namespace chromeos {
 #define LOGIN_LOG(level)                                   \
   DEVICE_LOG(::chromeos::device_event_log::LOG_TYPE_LOGIN, \
              ::chromeos::device_event_log::LOG_LEVEL_##level)
+#define USB_LOG(level)                                   \
+  DEVICE_LOG(::chromeos::device_event_log::LOG_TYPE_USB, \
+             ::chromeos::device_event_log::LOG_LEVEL_##level)
 
 // Generally prefer the above macros unless |type| or  |level| is not constant.
 
@@ -63,6 +66,8 @@ enum LogType {
   LOG_TYPE_POWER,
   // Login related events.
   LOG_TYPE_LOGIN,
+  // USB device related events (i.e. device/usb).
+  LOG_TYPE_USB,
   // Used internally
   LOG_TYPE_UNKNOWN
 };