pt 1 in reviving the android build (copied from pm 28a1, wish me luck)

mobile/android/thirdparty/ch/boye/httpclientandroidlib/client/cache/HttpCacheUpdateCallback.java

@@ -0,0 +1,52 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package ch.boye.httpclientandroidlib.client.cache;
+
+import java.io.IOException;
+
+/**
+ * Used for atomically updating entries in a {@link HttpCacheStorage}
+ * implementation. The current entry (if any) is fed into an implementation
+ * of this interface, and the new, possibly updated entry (if any)
+ * should be returned.
+ */
+public interface HttpCacheUpdateCallback {
+
+    /**
+     * Returns the new cache entry that should replace an existing one.
+     *
+     * @param existing
+     *            the cache entry currently in-place in the cache, possibly
+     *            <code>null</code> if nonexistent
+     * @return the cache entry that should replace it, again,
+     *         possibly <code>null</code> if the entry should be deleted
+     *
+     * @since 4.1
+     */
+    HttpCacheEntry update(HttpCacheEntry existing) throws IOException;
+
+}