Add KeyPairGenerator for Android keystore

This allows end-users to generate keys in the keystore without the
private part of the key ever needing to leave the device. The generation
process also generates a self-signed certificate.

Change-Id: I114ffb8e0cbe3b1edaae7e69e8aa578cb835efc9

keystore/java/android/security/AndroidKeyStoreProvider.java

@@ -29,6 +29,11 @@ public class AndroidKeyStoreProvider extends Provider {
     public AndroidKeyStoreProvider() {
         super(PROVIDER_NAME, 1.0, "Android KeyStore security provider");
 
+        // java.security.KeyStore
         put("KeyStore." + AndroidKeyStore.NAME, AndroidKeyStore.class.getName());
+
+        // java.security.KeyPairGenerator
+        put("KeyPairGenerator." + AndroidKeyPairGenerator.NAME,
+                AndroidKeyPairGenerator.class.getName());
     }
 }