Tighten override for the specific list to avoid calling every call "g…

…et" on generic lists (specificially LinkedList) in a loop.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=242905286

src/com/google/javascript/rhino/jstype/UnionTypeBuilder.java

@@ -157,7 +157,9 @@ public UnionTypeBuilder addAlternates(Collection<JSType> c) {
     return this;
   }
 
-  public UnionTypeBuilder addAlternates(List<JSType> list) {
+  // A specific override that avoid creating an iterator.  This version is currently used when
+  // adding a union as an alternate.
+  public UnionTypeBuilder addAlternates(ImmutableList<JSType> list) {
     for (int i = 0; i < list.size(); i++) {
       addAlternate(list.get(i));
     }