Declare event to be of type goog.debug.Trace_.Event_.
Declare event to be of type goog.debug.Trace_.Event_.

This allows NTI to declare the properties on event as properties of goog.debug.Trace_.Event_, and eliminates 10 inexistent-property warnings in Closure.

PUBLIC=same
RELNOTES:n/a

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130153976

redforks/closure-library,Medium/closure-library,teppeis/closure-library,joeltine/closure-library,codyebberson/closure-library,google/closure-library,ikabirov/closure-library,codyebberson/closure-library,ChadKillingsworth/closure-library,Medium/closure-library,joeltine/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,ikabirov/closure-library,Medium/closure-library,teppeis/closure-library,teppeis/closure-library,codyebberson/closure-library,lucidsoftware/closure-library,joeltine/closure-library,codyebberson/closure-library,joeltine/closure-library,platinumpixs/google-closure-library,google/closure-library,ChadKillingsworth/closure-library,google/closure-library,ChadKillingsworth/closure-library,platinumpixs/google-closure-library,ikabirov/closure-library,redforks/closure-library,platinumpixs/google-closure-library,redforks/closure-library,google/closure-library,teppeis/closure-library,Medium/closure-library,lucidsoftware/closure-library,ikabirov/closure-library,ChadKillingsworth/closure-library,platinumpixs/google-closure-library,redforks/closure-library,google/closure-library