Under J2CL, make EnumMultiset work. Previously, it was present but failed at runtime.

The easiest fix I could find was to change the GWT/J2CL implementation to use `AbstractMapBasedMultiset`. It's possible that that performs worse than the existing custom multiset implementation under GWT, but I don't know. It at least has the virtue of working under J2CL.

RELNOTES=`collect`: Under j2cl, made `EnumMultiset` work. Previously, it was present but failed at runtime.
PiperOrigin-RevId: 535711434

Author: cpovirk

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/EnumMultiset.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2007 The Guava Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.google.common.collect;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.collect.Platform.getDeclaringClassOrObjectForJ2cl;
+
+import com.google.common.annotations.GwtCompatible;
+import com.google.common.annotations.J2ktIncompatible;
+import java.io.Serializable;
+import java.util.EnumMap;
+import java.util.Iterator;
+
+@GwtCompatible(emulated = true)
+@J2ktIncompatible
+@ElementTypesAreNonnullByDefault
+public final class EnumMultiset<E extends Enum<E>> extends AbstractMapBasedMultiset<E>
+    implements Serializable {
+  public static <E extends Enum<E>> EnumMultiset<E> create(Class<E> type) {
+    return new EnumMultiset<>(new EnumMap<E, Count>(type));
+  }
+
+  public static <E extends Enum<E>> EnumMultiset<E> create(Iterable<E> elements) {
+    Iterator<E> iterator = elements.iterator();
+    checkArgument(iterator.hasNext(), "EnumMultiset constructor passed empty Iterable");
+    EnumMap<E, Count> map = new EnumMap<>(getDeclaringClassOrObjectForJ2cl(iterator.next()));
+    EnumMultiset<E> multiset = new EnumMultiset<>(map);
+    Iterables.addAll(multiset, elements);
+    return multiset;
+  }
+
+  public static <E extends Enum<E>> EnumMultiset<E> create(Iterable<E> elements, Class<E> type) {
+    EnumMultiset<E> result = create(type);
+    Iterables.addAll(result, elements);
+    return result;
+  }
+
+  /** Creates an empty {@code EnumMultiset}. */
+  private EnumMultiset(EnumMap<E, Count> map) {
+    super(map);
+  }
+}