docs($parse): add todo note

Author: IgorMinar

src/ng/parse.js

@@ -616,6 +616,7 @@ Parser.prototype = {
     if ((token = this.expect('?'))) {
       middle = this.assignment();
       if ((token = this.expect(':'))) {
+        // TODO(perf): merge ternary and ternaryFn?
         return this.ternaryFn(left, middle, this.assignment());
       } else {
         this.throwError('expected :', token);