Implement A/B experiment for anti-DDoS.

chrome/browser/ui/webui/net_internals_ui.cc

Index: chrome/browser/ui/webui/net_internals_ui.cc
diff --git a/chrome/browser/ui/webui/net_internals_ui.cc b/chrome/browser/ui/webui/net_internals_ui.cc
index cd8d09d9fb9e1398292236575f8ad2058ca8a189..34eb05546a776fa75f34fec660f3ce33621d9ae5 100644
--- a/chrome/browser/ui/webui/net_internals_ui.cc
+++ b/chrome/browser/ui/webui/net_internals_ui.cc
@@ -15,6 +15,7 @@
 #include "base/file_util.h"
 #include "base/memory/singleton.h"
 #include "base/message_loop.h"
+#include "base/metrics/field_trial.h"  // TODO(joi): Remove after experiment.
 #include "base/path_service.h"
 #include "base/string_number_conversions.h"
 #include "base/string_piece.h"
@@ -177,6 +178,7 @@ class NetInternalsMessageHandler
   // Javascript message handlers.
   void OnRendererReady(const ListValue* list);
   void OnEnableHttpThrottling(const ListValue* list);
+  void OnDisableThrottlingExperiments(const ListValue* list);
 #ifdef OS_CHROMEOS
   void OnRefreshSystemLogs(const ListValue* list);
   void OnGetSystemLog(const ListValue* list);
@@ -272,6 +274,11 @@ class NetInternalsMessageHandler
   // be accessed on the UI thread.
   BooleanPrefMember http_throttling_enabled_;
 
+  // The pref member that determines whether experimentation on HTTP throttling
+  // is allowed (this becomes false once the user explicitly sets the
+  // feature to on or off).
+  BooleanPrefMember http_throttling_may_experiment_;
+
   // OnRendererReady invokes this callback to do the part of message handling
   // that needs to happen on the IO thread.
   scoped_ptr<WebUI::MessageCallback> renderer_ready_io_callback_;
@@ -545,8 +552,10 @@ WebUIMessageHandler* NetInternalsMessageHandler::Attach(WebUI* web_ui) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   PrefService* pref_service = web_ui->GetProfile()->GetPrefs();
-  http_throttling_enabled_.Init(prefs::kHttpThrottlingEnabled, pref_service,
-                                this);
+  http_throttling_enabled_.Init(
+      prefs::kHttpThrottlingEnabled, pref_service, this);
+  http_throttling_may_experiment_.Init(
+      prefs::kHttpThrottlingMayExperiment, pref_service, NULL);
 
   proxy_ = new IOThreadImpl(this->AsWeakPtr(), g_browser_process->io_thread(),
                             web_ui->GetProfile()->GetRequestContext());
@@ -669,6 +678,11 @@ void NetInternalsMessageHandler::RegisterMessages() {
   web_ui_->RegisterMessageCallback(
       "enableHttpThrottling",
       NewCallback(this, &NetInternalsMessageHandler::OnEnableHttpThrottling));
+  web_ui_->RegisterMessageCallback(
+      "disableThrottlingExperiments",
+      NewCallback(
+          this,
+          &NetInternalsMessageHandler::OnDisableThrottlingExperiments));
 }
 
 void NetInternalsMessageHandler::CallJavascriptFunction(
@@ -720,6 +734,21 @@ void NetInternalsMessageHandler::OnEnableHttpThrottling(const ListValue* list) {
   http_throttling_enabled_.SetValue(enable);
 }
 
+void NetInternalsMessageHandler::OnDisableThrottlingExperiments(

[yzshen1, 2011/06/08 00:56:51]

The logic within this method can be put in the method OnEnableHttpThrottling, so
that you don't need to modify *.js files, and it is more clear.

[Jói, 2011/06/08 16:44:47]

You're right. I thought this method was also used at startup  (without user
action) but was confusing it with NetPrefObserver::ApplySettings().

I've removed the additional message and handler function.

+    const ListValue* list) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  if (http_throttling_may_experiment_.GetValue()) {
+    http_throttling_may_experiment_.SetValue(false);
+
+    // Disable the ongoing trial so that histograms after this point
+    // show as being in the "Default" group of the trial.
+    base::FieldTrial* trial = base::FieldTrialList::Find("ThrottlingEnabled");
+    if (trial)
+      trial->Disable();

[yzshen1, 2011/06/08 00:56:51]

It may be better to move the part of disabling the trial to
NetPrefObserver::ApplySettings().

[Jói, 2011/06/08 16:44:47]

I can't do that because that method gets called not only on user action but also
just at the startup of Chrome - so it's not a signal that the user changed the
setting.

Strictly speaking, I _could_ do it there when pref_name is not NULL, but it
feels a bit brittle to do it this way.  The user gesture is much more apparent
in the NetInternalsMessageHandler::OnEnableHttpThrottling which is only used as
a handler for explicit user action.

[yzshen1, 2011/06/08 16:55:54]

Makes sense. Thanks for explaining.
On 2011/06/08 16:44:47, Jói wrote:

+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 //
 // NetInternalsMessageHandler::ReadLogFileTask