Add missing license boilerplate.

Change-Id: I3f5dd60d16618856f0c4103afff2376fbff0c94d
ORIGINAL_AUTHOR=Thai Duong <thaidn@google.com>
GitOrigin-RevId: ab3c1653bf46cab458548b858462ffc4050c704b

java/src/main/java/com/google/crypto/tink/subtle/DJBCipher.java

+// Copyright 2017 Google Inc.
+//
+// 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.crypto.tink.subtle;
 
 import java.nio.ByteBuffer;