[cronet] Expose API to set experimental options

components/cronet/ios/cronet_environment.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/cronet/ios/cronet_environment.h"
 
 #include <utility>
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
@@ skipping 203 matching lines @@
                                     int port,
                                     int alternate_port) {
   DCHECK(port == alternate_port);
   quic_hints_.push_back(net::HostPortPair(host, port));
 }
 
 CronetEnvironment::CronetEnvironment(const std::string& user_agent,
                                      bool user_agent_partial)
     : http2_enabled_(false),
       quic_enabled_(false),
+      experimental_options_("{}"),

[mef, 2017/03/21 20:44:57]

nit: I don't think this is necessary as it is covered on objC side and empty
string appears to be a valid default.

[lilyhoughton, 2017/03/22 13:40:55]

Done.  Should I have Obj-C default be an empty string as well?

How much should we be thinking about what the use of C++ API without Obj-C will
look like/having sane defaults for that?

[mef, 2017/03/22 19:18:26]

 I think so. It seems that on Android they default to empty string:
https://cs.chromium.org/chromium/src/components/cronet/android/java/src/org/c...
That would be nice to reduce confusion.

       http_cache_(URLRequestContextConfig::HttpCacheType::DISK),
       user_agent_(user_agent),
       user_agent_partial_(user_agent_partial),
       net_log_(new net::NetLog) {}
 
 void CronetEnvironment::Start() {
   // Threads setup.
   network_cache_thread_.reset(new base::Thread("Chrome Network Cache Thread"));
   network_cache_thread_->StartWithOptions(
       base::Thread::Options(base::MessageLoop::TYPE_IO, 0));
@@ skipping 52 matching lines @@
   cache_path = cache_path.Append(FILE_PATH_LITERAL("cronet"));
 
   URLRequestContextConfigBuilder context_config_builder;
   context_config_builder.enable_quic = quic_enabled_;   // Enable QUIC.
   context_config_builder.enable_spdy = http2_enabled_;  // Enable HTTP/2.
   context_config_builder.http_cache = http_cache_;      // Set HTTP cache
   context_config_builder.storage_path =
       cache_path.value();  // Storage path for http cache and cookie storage.
   context_config_builder.user_agent =
       user_agent_;  // User-Agent request header field.
+  context_config_builder.experimental_options =

[mef, 2017/03/21 20:44:58]

I think we also need to do something similar to
CronetURLRequestContextAdapter::GetNetLogInfo() in order to be able to log those
as part of net log :
https://cs.chromium.org/chromium/src/components/cronet/android/cronet_url_req...

Check with xunjieli@, It should be ok to do as followup CL depending on how big
are required changes.

[lilyhoughton, 2017/03/22 13:40:55]

Acknowledged.

+      experimental_options_;  // Set experimental Cronet options.
   context_config_builder.mock_cert_verifier = std::move(
       mock_cert_verifier_);  // MockCertVerifier to use for testing purposes.
   std::unique_ptr<URLRequestContextConfig> config =
       context_config_builder.Build();
 
   net::URLRequestContextBuilder context_builder;
 
   context_builder.set_accept_language(accept_language_);
 
   config->ConfigureURLRequestContextBuilder(&context_builder, net_log_.get(),
@@ skipping 70 matching lines @@
   event->Signal();
 }
 
 std::string CronetEnvironment::getDefaultQuicUserAgentId() const {
   return base::SysNSStringToUTF8([[NSBundle mainBundle]
              objectForInfoDictionaryKey:@"CFBundleDisplayName"]) +
          " Cronet/" + CRONET_VERSION;
 }
 
 }  // namespace cronet