Added a field trial (finch experiment) to disable SPDY for x% of users.

chrome/browser/io_thread.cc

 // Copyright (c) 2012 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 "chrome/browser/io_thread.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 85 matching lines @@
 
 // The IOThread object must outlive any tasks posted to the IO thread before the
 // Quit task, so base::Bind() calls are not refcounted.
 
 namespace {
 
 const char kQuicFieldTrialName[] = "QUIC";
 const char kQuicFieldTrialEnabledGroupName[] = "Enabled";
 const char kQuicFieldTrialHttpsEnabledGroupName[] = "HttpsEnabled";
 
+const char kSpdyFieldTrialName[] = "SPDY";
+const char kSpdyFieldTrialDisabledGroupName[] = "SpdyDisabled";
+
 #if defined(OS_MACOSX) && !defined(OS_IOS)
 void ObserveKeychainEvents() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   net::CertDatabase::GetInstance()->SetMessageLoopForKeychainEvents();
 }
 #endif
 
 // Used for the "system" URLRequestContext.
 class SystemURLRequestContext : public net::URLRequestContext {
  public:
@@ skipping 563 matching lines @@
 void IOThread::InitializeNetworkOptions(const CommandLine& command_line) {
   if (command_line.HasSwitch(switches::kEnableFileCookies)) {
     // Enable cookie storage for file:// URLs.  Must do this before the first
     // Profile (and therefore the first CookieMonster) is created.
     net::CookieMonster::EnableFileScheme();
   }
 
   // Only handle use-spdy command line flags if "spdy.disabled" preference is
   // not disabled via policy.
   if (!is_spdy_disabled_by_policy_) {
+    std::string spdy_trial_group;
+
     if (command_line.HasSwitch(switches::kEnableIPPooling))
       globals_->enable_spdy_ip_pooling.set(true);
 
     if (command_line.HasSwitch(switches::kDisableIPPooling))
       globals_->enable_spdy_ip_pooling.set(false);
 
     if (command_line.HasSwitch(switches::kEnableSpdyCredentialFrames))
       globals_->enable_spdy_credential_frames.set(true);
 
     if (command_line.HasSwitch(switches::kEnableWebSocketOverSpdy)) {
       // Enable WebSocket over SPDY.
       net::WebSocketJob::set_websocket_over_spdy_enabled(true);
+    } else {
+      spdy_trial_group =
+          base::FieldTrialList::FindFullName(kSpdyFieldTrialName);

[Alexei Svitkine (slow), 2013/10/01 13:55:31]

Why is this here?

In your pending config CL, you have a group for kEnableWebSocketOverSpdy. But in
this initialization code, it looks like it doesn't actually enable spdy
explicitly... its still based on the flags below.

So it looks like you should just do this right above the if
(command_line.HasSwitch(switches::kUseSpdy)) line (since you have entries for
all of those groups). Or let me know what I'm missing here...

[ramant (doing other things), 2013/10/01 17:38:18]

If the command line kEnableWebSocketOverSpdy is selected, I didn't like to
disable SPDY. Reading the code as it is written here, I couldn't assert that
spdy_trial_group wouldn't be kSpdyFieldTrialDisabledGroupName if the above
command line is selected.

The other alternative is to check for
"command_line.HasSwitch(switches::kEnableWebSocketOverSpdy" at line# 738 and if
the command line is set, then default to Spdy3.1.

As per our discussion offline, added the check at line#738.

     }
+
     if (command_line.HasSwitch(switches::kMaxSpdyConcurrentStreams)) {
       globals_->max_spdy_concurrent_streams_limit.set(
           GetSwitchValueAsInt(command_line,
                               switches::kMaxSpdyConcurrentStreams));
     }
     if (command_line.HasSwitch(switches::kTrustedSpdyProxy)) {
       globals_->trusted_spdy_proxy.set(
           command_line.GetSwitchValueASCII(switches::kTrustedSpdyProxy));
     }
     if (command_line.HasSwitch(switches::kIgnoreUrlFetcherCertRequests))
       net::URLFetcher::SetIgnoreCertificateRequests(true);
 
     if (command_line.HasSwitch(switches::kUseSpdy)) {
       std::string spdy_mode =
           command_line.GetSwitchValueASCII(switches::kUseSpdy);
       EnableSpdy(spdy_mode);
     } else if (command_line.HasSwitch(switches::kEnableHttp2Draft04)) {
       net::HttpStreamFactory::EnableNpnHttp2Draft04();
     } else if (command_line.HasSwitch(switches::kEnableSpdy4a2)) {
       net::HttpStreamFactory::EnableNpnSpdy4a2();
     } else if (command_line.HasSwitch(switches::kDisableSpdy31)) {
       net::HttpStreamFactory::EnableNpnSpdy3();
     } else if (command_line.HasSwitch(switches::kEnableNpn)) {
       net::HttpStreamFactory::EnableNpnSpdy();
     } else if (command_line.HasSwitch(switches::kEnableNpnHttpOnly)) {
       net::HttpStreamFactory::EnableNpnHttpOnly();
     } else {
-      // Use SPDY/3.1 by default.
-      net::HttpStreamFactory::EnableNpnSpdy31();
+      if (spdy_trial_group == kSpdyFieldTrialDisabledGroupName) {
+         net::HttpStreamFactory::set_spdy_enabled(false);
+      } else {
+        // Use SPDY/3.1 by default.
+        net::HttpStreamFactory::EnableNpnSpdy31();
+      }
     }
+  } else {
+    base::FieldTrial* trial = base::FieldTrialList::Find(kSpdyFieldTrialName);

[Alexei Svitkine (slow), 2013/10/01 13:55:31]

Nit: I'd negate the conditional and put this at the beginning to make this part
clearer.

Alternatively, if you can guarantee that nothing else calls FindFullName() on
this trial, then you can omit this (since it won't be marked active).

[ramant (doing other things), 2013/10/01 17:38:18]

Negated the check.

Done.

+    if (trial)
+      trial->Disable();
   }
 
   // TODO(rch): Make the client socket factory a per-network session
   // instance, constructed from a NetworkSession::Params, to allow us
   // to move this option to IOThread::Globals &
   // HttpNetworkSession::Params.
   if (command_line.HasSwitch(switches::kEnableTcpFastOpen))
     net::SetTCPFastOpenEnabled(true);
 }
 
@@ skipping 273 matching lines @@
   if (command_line.HasSwitch(switches::kDisableQuicHttps))
     return false;
 
   if (command_line.HasSwitch(switches::kEnableQuicHttps))
     return true;
 
   // HTTPS over QUIC should only be enabled if we are in the https
   // field trial group.
   return quic_trial_group == kQuicFieldTrialHttpsEnabledGroupName;
 }