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 5665b0ff88ebc3a6fc36e301b82eb7fb27507cd9..b01a30054dc6ca5091f5c58f591565fd6339e694 100644
--- a/extensions/common/cast/cast_cert_validator.cc
+++ b/extensions/common/cast/cast_cert_validator.cc
@@ -292,6 +292,11 @@ std::unique_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