Add a hook to inject trusted Cast roots for testing purposes.

extensions/common/cast/cast_cert_validator.cc

Index: extensions/common/cast/cast_cert_validator.cc
diff --git a/extensions/common/cast/cast_cert_validator.cc b/extensions/common/cast/cast_cert_validator.cc
index f80b1063d132cecaa7cbd1f2dc177230e5d6f621..2b7add252f035700d840691f9cdfcc9400aeac2c 100644
--- a/extensions/common/cast/cast_cert_validator.cc
+++ b/extensions/common/cast/cast_cert_validator.cc
@@ -289,6 +289,11 @@ scoped_ptr<CertVerificationContext> CertVerificationContextImplForTest(
       new CertVerificationContextImpl(net::der::Input(spki), "CommonName"));
 }
 
+bool AddTrustAnchorForTest(const uint8_t* data, size_t length) {
+  return CastTrustStore::Get().AddTrustedCertificateWithoutCopying(data,
+                                                                   length);
+}
+
 }  // namespace cast_crypto
 }  // namespace api
 }  // namespace extensions