Expose findByIssuerAndSignature

This will be used to create a custom conscrypt TrustedCertificateStore
to avoid loading all of the trusted certificates into memory in a
keystore.

Change-Id: Iaf54b691393ecadae6c7ff56b8adc6a2a2923d29

tests/NetworkSecurityConfigTest/src/android/security/net/config/TestCertificateSource.java

@@ -44,4 +44,12 @@ public class TestCertificateSource implements CertificateSource {
         }
         return anchor.getTrustedCert();
     }
+
+    public X509Certificate findByIssuerAndSignature(X509Certificate cert) {
+        java.security.cert.TrustAnchor anchor = mIndex.findByIssuerAndSignature(cert);
+        if (anchor == null) {
+            return null;
+        }
+        return anchor.getTrustedCert();
+    }
 }