Set up field trials for SSL read/write buffer sizes.

net/socket/ssl_client_socket_impl.cc

Index: net/socket/ssl_client_socket_impl.cc
diff --git a/net/socket/ssl_client_socket_impl.cc b/net/socket/ssl_client_socket_impl.cc
index 80ff994982f2d3e804266d8623bae1dd2e90b0d4..c775c3edd5568258e30e61b04eb84a7e9521a1fa 100644
--- a/net/socket/ssl_client_socket_impl.cc
+++ b/net/socket/ssl_client_socket_impl.cc
@@ -20,6 +20,7 @@
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/profiler/scoped_tracker.h"
@@ -85,7 +86,7 @@ const int kNoPendingResult = 1;
 const char kDefaultSupportedNPNProtocol[] = "http/1.1";
 
 // Default size of the internal BoringSSL buffers.
-const int KDefaultOpenSSLBufferSize = 17 * 1024;
+const int kDefaultOpenSSLBufferSize = 17 * 1024;
 
 // TLS extension number use for Token Binding.
 const unsigned int kTbExtNum = 24;
@@ -929,10 +930,29 @@ int SSLClientSocketImpl::Init() {
   if (session)
     SSL_set_session(ssl_, session.get());
 
+  // Get read and write buffer sizes from field trials, if possible. If values
+  // not present, use default.  Also make sure values are in reasonable range.
+  int send_buffer_size;
+  if (!base::StringToInt(
+          base::FieldTrialList::FindFullName("SSLBufferSizeSend"),
+          &send_buffer_size)) {

[jwd, 2016/06/28 15:35:12]

I'd prefer you use variation params instead of the group name for specifying the
buffer size.

[mmenke, 2016/06/28 18:47:21]

Unfortunately, net/ can depend on components/.

[mmenke, 2016/06/28 18:47:59]

can't, rather

[jwd, 2016/06/28 19:05:16]

Ah, ok, so in that case, I'm fine how it is. StringToInt should give you enough
flexibility to rename groups and still have them parse correctly. You'll
obviously just need to take some care if you ever do need to rename groups.
(group renaming can be useful if you want have a new phase of experimentation
and you don't want it to mix the data with the old.)

If you ARE interested in using params, you can add to chrome_network_delegate.h
to get access to that data.

[mmenke, 2016/06/28 19:18:23]

Unfortunately, this deep in the network stack, we don't have access to that,
either.  Client socket pools can actually be shared between URLRequestContexts
with different NetworkDelegates, too, which can get very troublesome (And is
really a bad design).

Thanks for the suggestions, though.  I suppose the exact size doesn't really
matter, so we could just hack around that by using off-by-one values, though
that seems weird.

StringToInt may even be able to handle suffixes...  i.e. "4096 Trial 2", though
I'm not positive of that.

[jwd, 2016/06/28 19:23:22]

Ah, none of my suggestions work! Oh well...
Yeah, suffixes is what I was thinking. The comments for StringToInt lead me to
believe this would work.

+    send_buffer_size = kDefaultOpenSSLBufferSize;
+  }
+  send_buffer_size = std::max(send_buffer_size, 1000);
+  send_buffer_size = std::min(send_buffer_size, 2 * kDefaultOpenSSLBufferSize);
   send_buffer_ = new GrowableIOBuffer();
-  send_buffer_->SetCapacity(KDefaultOpenSSLBufferSize);
+  send_buffer_->SetCapacity(send_buffer_size);
+
+  int recv_buffer_size;
+  if (!base::StringToInt(
+          base::FieldTrialList::FindFullName("SSLBufferSizeRecv"),
+          &recv_buffer_size)) {
+    recv_buffer_size = kDefaultOpenSSLBufferSize;
+  }
+  recv_buffer_size = std::max(recv_buffer_size, 1000);
+  recv_buffer_size = std::min(recv_buffer_size, 2 * kDefaultOpenSSLBufferSize);
   recv_buffer_ = new GrowableIOBuffer();
-  recv_buffer_->SetCapacity(KDefaultOpenSSLBufferSize);
+  recv_buffer_->SetCapacity(recv_buffer_size);
 
   BIO* ssl_bio = NULL;