message: Minor fixes in KeyTypeManager.
  Use KeyProtoT instead of KeyT to be clear that this is always a proto.
  Use "extends MessageLite" where appropriate.
diff: @@ -57,7 +57,7 @@ import java.util.Set;
  @Alpha
  public abstract class KeyTypeManager<KeyProtoT extends MessageLite> {
  /** A PrimitiveFactory knows how to create primitives from a given key. */
  - protected abstract static class PrimitiveFactory<PrimitiveT, KeyT> {
  + protected abstract static class PrimitiveFactory<PrimitiveT, KeyProtoT extends MessageLite> {
  private final Class<PrimitiveT> clazz;
  public PrimitiveFactory(Class<PrimitiveT> clazz) {
  @@ -78,7 +78,7 @@ public abstract class KeyTypeManager<KeyProtoT extends MessageLite> {
  * PublicKeyVerify}, {@code DeterministicAead}, {@code HybridEncrypt}, and {@code HybridDecrypt}
  * this should be a primitive which <b>ignores</b> the output prefix and assumes "RAW".
  */
  - public abstract PrimitiveT getPrimitive(KeyT key) throws GeneralSecurityException;
  + public abstract PrimitiveT getPrimitive(KeyProtoT key) throws GeneralSecurityException;
  }
  private final Class<KeyProtoT> clazz;
  @@ -190,7 +190,8 @@ public abstract class KeyTypeManager<KeyProtoT extends MessageLite> {
  * be able to generate keys. In particular, in this case it needs to have some KeyFormat protocol
  * buffer which can be validated, parsed, and from which a key can be generated.
  */
  - public abstract static class KeyFactory<KeyFormatProtoT extends MessageLite, KeyT> {
  + public abstract static class KeyFactory<
  + KeyFormatProtoT extends MessageLite, KeyProtoT extends MessageLite> {
  private final Class<KeyFormatProtoT> clazz;
  public KeyFactory(Class<KeyFormatProtoT> clazz) {
  this.clazz = clazz;
  @@ -235,7 +236,7 @@ public abstract class KeyTypeManager<KeyProtoT extends MessageLite> {
  throws InvalidProtocolBufferException;
  /** Creates a new key from a given format. */
  - public abstract KeyT createKey(KeyFormatProtoT keyFormat) throws GeneralSecurityException;
  + public abstract KeyProtoT createKey(KeyFormatProtoT keyFormat) throws GeneralSecurityException;
  /**
  * Derives a new key from a given format, using the given {@code pseudoRandomness}.
  @@ -251,7 +252,7 @@ public abstract class KeyTypeManager<KeyProtoT extends MessageLite> {
  * <p>Not every KeyTypeManager needs to implement this; if not implemented a {@link
  * GeneralSecurityException} will be thrown.
  */
  - public KeyT deriveKey(KeyFormatProtoT keyFormat, InputStream pseudoRandomness)
  + public KeyProtoT deriveKey(KeyFormatProtoT keyFormat, InputStream pseudoRandomness)
  throws GeneralSecurityException {
  throw new GeneralSecurityException("deriveKey not implemented for key of type " + clazz);
  }
  