Breaking Change: merge BoringSSL branch into master

tests/standalone/io/certificates/README

+    This directory, tests/standalone/io/certificates, contains the
+X509 TLS certificates and private keys needed to run tests of Dart's
+secure networking code.  The SecureSocket and SecureServer classes
+are tested by making TLS (formerly called SSL) connections, secured
+by certificates created by the create_test_certificates script in
+the parent directory, and copied into this directory.
+
+server_chain.pem:
+  Contains the chain of certificates, from the self-signed
+test certificate authority, through the intermediate CA, to the server
+certificate, used on the server side of a test connection.
+
+server_key.pem:
+  Contains the private key for the server certificate
+
+trusted_certs.pem:
+  Contains the self-signed certificate of the test certificate authority.
+This certificate is set as "trusted" by the client side of the connection
+in its SecurityContext object, so that a verified TLS connection to the
+server can be made.
+
+untrusted_server_chain.pem:
+  Contains a chain of certificates, from a different self-signed
+test certificate authority, through an intermediate CA, to a server
+certificate, used on the server side of a test connection that is intended
+to fail because the client does not accept this certificate authority
+
+untrusted_server_key.pem:
+  Contains the private key for the untrusted server certificate 
+in untrusted_server_chain.pem
+