Implement QUIC key extraction.

net/quic/quic_crypto_stream.h

Index: net/quic/quic_crypto_stream.h
diff --git a/net/quic/quic_crypto_stream.h b/net/quic/quic_crypto_stream.h
index 2c61a18fe782dcddad5888201485dff12bb8f6bd..e9d575ccc29444c92399d7f8b0b3b37757eed08a 100644
--- a/net/quic/quic_crypto_stream.h
+++ b/net/quic/quic_crypto_stream.h
@@ -46,6 +46,15 @@ class NET_EXPORT_PRIVATE QuicCryptoStream
   // TODO(wtc): return a success/failure status.
   void SendHandshakeMessage(const CryptoHandshakeMessage& message);
 
+  // Performs key extraction to derive a new secret of |result_len| bytes
+  // dependent on |label|, |context|, and the stream's negotiated subkey secret.
+  // Returns false if the handshake has not been confirmed or the parameters are
+  // invalid (e.g. |label| contains null bytes); returns true on success.
+  bool ExportKeyingMaterial(base::StringPiece label,
+                            base::StringPiece context,
+                            size_t result_len,
+                            std::string* result) const;
+
   bool encryption_established() const { return encryption_established_; }
   bool handshake_confirmed() const { return handshake_confirmed_; }