Automated g4 rollback of changelist 139602401.

*** Reason for rollback ***

breaks jdossier because it introduces a binary incompatibility and jdossier is built against one version of rhino and runs against head... which is sad and should be fixed

*** Original change description ***

Change UnionType to hold a List instead of a Collection for the alternates and switch most accessors to do indexed iteration.

heap profiling showed that the iteration in JsType.checkEquivalenceHelper was allocating lots of iterators. This is an easy, if slightly annoying, way to make these operations a little cheaper.

***

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139623208

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

@@ -44,14 +44,13 @@
 import com.google.common.base.Preconditions;
 import com.google.common.base.Predicate;
 import com.google.common.collect.HashBasedTable;
-import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableList;
 import com.google.javascript.rhino.ErrorReporter;
 import com.google.javascript.rhino.JSDocInfo;
 import com.google.javascript.rhino.TypeI;
 import java.io.Serializable;
 import java.util.Comparator;
 import java.util.IdentityHashMap;
-import java.util.List;
 
 /**
  * Represents JavaScript value types.<p>
@@ -79,8 +78,8 @@ public abstract class JSType implements TypeI, Serializable {
   private static final CanCastToVisitor CAN_CAST_TO_VISITOR =
       new CanCastToVisitor();
 
-  private static final ImmutableSet<String> COVARIANT_TYPES =
-      ImmutableSet.of("Object", "IArrayLike", "Array");
+  private static final ImmutableList<String> COVARIANT_TYPES =
+      ImmutableList.of("Object", "IArrayLike", "Array");
 
   /**
    * Total ordering on types based on their textual representation.
@@ -303,9 +302,7 @@ public boolean containsArray() {
     // Check if this is a union that contains an array
     if (this.isUnionType()) {
       JSType arrayType = registry.getNativeType(JSTypeNative.ARRAY_TYPE);
-      List<JSType> alternates = this.toMaybeUnionType().getAlternates();
-      for (int i = 0; i < alternates.size(); i++) {
-        JSType alternate = alternates.get(i);
+      for (JSType alternate : this.toMaybeUnionType().getAlternates()) {
         if (alternate.isSubtype(arrayType)) {
           return true;
         }
@@ -1129,9 +1126,7 @@ static JSType filterNoResolvedType(JSType type) {
     } else if (type.isUnionType()) {
       UnionType unionType = type.toMaybeUnionType();
       boolean needsFiltering = false;
-      List<JSType> alternates = unionType.getAlternates();
-      for (int i = 0; i < alternates.size(); i++) {
-        JSType alt = alternates.get(i);
+      for (JSType alt : unionType.getAlternates()) {
         if (alt.isNoResolvedType()) {
           needsFiltering = true;
           break;
@@ -1411,10 +1406,8 @@ static boolean isSubtypeHelper(JSType thisType, JSType thatType,
     // unions
     if (thatType.isUnionType()) {
       UnionType union = thatType.toMaybeUnionType();
-      List<JSType> alternates = union.alternatesWithoutStucturalTyping;
-      // use indexed iteration to avoid iterator allocations
-      for (int i = 0; i < alternates.size(); i++) {
-        if (thisType.isSubtype(alternates.get(i), implicitImplCache, subtypingMode)) {
+      for (JSType element : union.alternatesWithoutStucturalTyping) {
+        if (thisType.isSubtype(element, implicitImplCache, subtypingMode)) {
           return true;
         }
       }