@java.lang.Override
  public int getSerializedSize() {
    int size = memoizedSize;
    if (size != -1) return size;

    size = 0;
    for (java.util.Map.Entry<java.lang.String, java.lang.String> entry :
        internalGetHeaders().getMap().entrySet()) {
      com.google.protobuf.MapEntry<java.lang.String, java.lang.String> headers__ =
          HeadersDefaultEntryHolder.defaultEntry
              .newBuilderForType()
              .setKey(entry.getKey())
              .setValue(entry.getValue())
              .build();
      size += com.google.protobuf.CodedOutputStream.computeMessageSize(1, headers__);
    }
    size += getUnknownFields().getSerializedSize();
    memoizedSize = size;
    return size;
  }
<pre>
Custom headers to pass into fetch request.
Headers must have a maximum of 3 key value pairs.
Each key value pair must have a maximum of 256 characters per key and 256
characters per value.
</pre>

<code>map&lt;string, string&gt; headers = 1;</code>
java-video-stitcher/proto-google-cloud-video-stitcher-v1/src/main/java/com/google/cloud/video/stitcher/v1/FetchOptions.java