[Smart Lock] Add error message strings for the "Tx Power too high" case.

chrome/common/extensions/api/easy_unlock_private.idl

Index: chrome/common/extensions/api/easy_unlock_private.idl
diff --git a/chrome/common/extensions/api/easy_unlock_private.idl b/chrome/common/extensions/api/easy_unlock_private.idl
index e7b87150e80875dfd3f3656c68325d97fe361c68..5e97e61da713ed9a3b9a7a14135fe22e4e3300fb 100644
--- a/chrome/common/extensions/api/easy_unlock_private.idl
+++ b/chrome/common/extensions/api/easy_unlock_private.idl
@@ -48,7 +48,12 @@ namespace easyUnlockPrivate {
     // transmission power is too high, indicating that the phone is (probably)
     // more than 1 foot away, and therefore is not allowed to unlock the device.
     TX_POWER_TOO_HIGH,
-    // The devie can be unlocked using Easy Unlock.
+    // A phone eligible to unlock the device is found; but (a) the phone is
+    // locked, and (b) the local device's transmission power is too high,
+    // indicating that the phone is (probably) more than 1 foot away, and
+    // therefore is not allowed to unlock the device.
+    PHONE_LOCKED_AND_TX_POWER_TOO_HIGH,
+    // The device can be unlocked using Easy Unlock.
     AUTHENTICATED
   };