Add an overload of spliterator() to the Android flavor of one of ou…

…r classes.

This is a further attempt to shake out any problems in advance of exposing "real" Java 8 APIs (google#6567). If something goes wrong with `spliterator()`, I think we could remove it without breaking callers: Either it's an override (in which case calls to it will continue to work after it's removed) or it's not (in which case Java 8 APIs aren't available, so calls to it would never have worked.)

RELNOTES=n/a
PiperOrigin-RevId: 603812702

android/guava/src/com/google/common/collect/ImmutableCollection.java

@@ -36,6 +36,8 @@
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Spliterator;
+import java.util.Spliterators;
 import javax.annotation.CheckForNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -176,13 +178,26 @@ public abstract class ImmutableCollection<E> extends AbstractCollection<E> imple
    * These are properties of the collection as a whole; SIZED and SUBSIZED are more properties of
    * the spliterator implementation.
    */
+  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})
+  // @IgnoreJRERequirement is not necessary because this compiles down to a constant.
+  // (which is fortunate because Animal Sniffer doesn't look for @IgnoreJRERequirement on fields)
+  static final int SPLITERATOR_CHARACTERISTICS =
+      Spliterator.IMMUTABLE | Spliterator.NONNULL | Spliterator.ORDERED;
 
   ImmutableCollection() {}
 
   /** Returns an unmodifiable iterator across the elements in this collection. */
   @Override
   public abstract UnmodifiableIterator<E> iterator();
 
+  @Override
+  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})
+  @IgnoreJRERequirement // used only from APIs with Java 8 types in them
+  // (not used within guava-android as of this writing, but we include it in the jar as a test)
+  public Spliterator<E> spliterator() {
+    return Spliterators.spliterator(this, SPLITERATOR_CHARACTERISTICS);
+  }
+
   private static final Object[] EMPTY_ARRAY = {};
 
   @Override