Bug 1529072 - JS Fuzzing: Add flag to fuzz harder than --ion-eager. r=jandem

Differential Revision: https://phabricator.services.mozilla.com/D20477

--HG--
extra : moz-landing-system : lando

js/src/shell/fuzz-flags.txt

@@ -33,6 +33,8 @@
 --ion-scalar-replacement=on
 --ion-sincos=off
 --ion-sincos=on
+--ion-warmup-threshold=0
+--ion-warmup-threshold=10
 --ion-warmup-threshold=100
 --no-native-regexp
 --nursery-strings=off