Add a new prefer_aes finch options for QUIC.

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index 7a02c5b9a1b2701935d9b76b05e55c62f8d31f9d..aefdc97f8cf5660d2abbec52ffdcc332b2c70327 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -189,6 +189,7 @@ class IOThread : public content::BrowserThreadDelegate {
     Optional<bool> quic_enable_connection_racing;
     Optional<bool> quic_enable_non_blocking_io;
     Optional<bool> quic_disable_disk_cache;
+    Optional<bool> quic_prefer_aes;
     Optional<int> quic_max_number_of_lossy_connections;
     Optional<float> quic_packet_loss_threshold;
     Optional<int> quic_socket_receive_buffer_size;
@@ -375,6 +376,9 @@ class IOThread : public content::BrowserThreadDelegate {
   static bool ShouldQuicDisableDiskCache(
       const VariationParameters& quic_trial_params);
 
+  // Returns true if QUIC should prefer AES-GCN even without hardware support.
+  static bool ShouldQuicPreferAes(const VariationParameters& quic_trial_params);
+
   // Returns the maximum number of QUIC connections with high packet loss in a
   // row after which QUIC should be disabled.  Returns 0 if the default value
   // should be used.