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

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index d2745b3148316620a4bde35bac99abf9b1ce5b5b..62b7763f51879f5ecfacaeb3ad9cd19f515a4bfc 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -103,6 +103,9 @@ const char kQuicFieldTrialName[] = "QUIC";
 const char kQuicFieldTrialEnabledGroupName[] = "Enabled";
 const char kQuicFieldTrialHttpsEnabledGroupName[] = "HttpsEnabled";
 
+const char kSpdyFieldTrialName[] = "SPDY";
+const char kSpdyFieldTrialDisabledGroupName[] = "Disabled";
+
 #if defined(OS_MACOSX) && !defined(OS_IOS)
 void ObserveKeychainEvents() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
@@ -726,8 +729,14 @@ void IOThread::InitializeNetworkOptions(const CommandLine& command_line) {
     } else if (command_line.HasSwitch(switches::kEnableNpnHttpOnly)) {
       net::HttpStreamFactory::EnableNpnHttpOnly();
     } else {
-      // Use SPDY/3.1 by default.
-      net::HttpStreamFactory::EnableNpnSpdy31();
+      std::string spdy_trial_group =
+          base::FieldTrialList::FindFullName(kSpdyFieldTrialName);

[Ryan Hamilton, 2013/09/28 13:58:40]

You need to make sure that you call FindFullName for every browser session, even
if it's disabled via command line flag.  You'll also need to add forcing flags
to the finch config.

You might want to ask the finch folks about what to do if spdy is disabled by
policy to make sure we account for that correctly.

[ramant (doing other things), 2013/09/29 23:41:32]

Done.
Will do.
CC'ed marcin finch advisor (will find from him about what to do if SPDY is
disabled via policy)

+      if (spdy_trial_group == kSpdyFieldTrialDisabledGroupName) {
+         net::HttpStreamFactory::set_spdy_enabled(false);
+      } else {
+        // Use SPDY/3.1 by default.
+        net::HttpStreamFactory::EnableNpnSpdy31();
+      }
     }
   }