Add DPM.hasKeyPair()

(trimmed down to only contain IKeyChainService.aidl change)

The method returns true if a private key and a user certifiate are
present in KeyChain under this alias.

Bug: 179180345
Test: atest com.android.cts.devicepolicy.MixedManagedProfileOwnerTest#testKeyManagement
Test: atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testDelegatedCertInstallerDirectly
Test: atest android.admin.cts.DevicePolicyManagerTest
Change-Id: I15ca6190db1ef4dbf0caabe9d46008d92f758df5
Merged-In: I15ca6190db1ef4dbf0caabe9d46008d92f758df5
diff --git a/keystore/java/android/security/IKeyChainService.aidl b/keystore/java/android/security/IKeyChainService.aidl
index 97da3cc..1ae6a63 100644
--- a/keystore/java/android/security/IKeyChainService.aidl
+++ b/keystore/java/android/security/IKeyChainService.aidl
@@ -46,6 +46,7 @@
     boolean installKeyPair(
         in byte[] privateKey, in byte[] userCert, in byte[] certChain, String alias, int uid);
     boolean removeKeyPair(String alias);
+    boolean containsKeyPair(String alias);
 
     // APIs used by Settings
     boolean deleteCaCertificate(String alias);