[cronet] Add member for QUIC user agent ID, with getter and setter.

components/cronet/ios/cronet_environment.mm

Index: components/cronet/ios/cronet_environment.mm
diff --git a/components/cronet/ios/cronet_environment.mm b/components/cronet/ios/cronet_environment.mm
index 62c8407aa863134ef03416e4a4c95733e2582e29..40defa199fbbf9d5a5354c3b930e777d46c21cd5 100644
--- a/components/cronet/ios/cronet_environment.mm
+++ b/components/cronet/ios/cronet_environment.mm
@@ -213,6 +213,7 @@ CronetEnvironment::CronetEnvironment(const std::string& user_agent,
                                      bool user_agent_partial)
     : http2_enabled_(false),
       quic_enabled_(false),
+      quic_user_agent_id_(""),

[mef, 2016/12/12 21:52:20]

std::string is initialized to empty string by default.

[lilyhoughton, 2016/12/13 15:10:22]

Done.

       user_agent_(user_agent),
       user_agent_partial_(user_agent_partial),
       net_log_(new net::NetLog) {}
@@ -271,7 +272,7 @@ void CronetEnvironment::InitializeOnNetworkThread() {
 
   std::unique_ptr<URLRequestContextConfig> config(new URLRequestContextConfig(
       quic_enabled_,                  // Enable QUIC.
-      "",                             // QUIC User Agent ID.
+      quic_user_agent_id_,            // QUIC User Agent ID.

[mef, 2016/12/12 21:52:20]

could call getDefault... here if |quic_user_agent_id_| is empty.

[lilyhoughton, 2016/12/13 15:10:22]

It should also check if |quic_enabled_| is true, to avoid an unnecessary
NSBundle call, right?

[mef, 2016/12/13 20:46:43]

Yes, good point.

       http2_enabled_,                 // Enable SPDY.
       false,                          // Enable SDCH
       URLRequestContextConfig::DISK,  // Type of http cache.