Add one-time randomization support for FieldTrial, and the ability to

content/renderer/renderer_main.cc

 // Copyright (c) 2011 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.
 
 #if defined(OS_MACOSX)
 #include <signal.h>
 #include <unistd.h>
 #endif  // OS_MACOSX
 
 #include "base/command_line.h"
@@ skipping 173 matching lines @@
   bool no_sandbox = parsed_command_line.HasSwitch(switches::kNoSandbox);
   platform.InitSandboxTests(no_sandbox);
 
   // Initialize histogram statistics gathering system.
   // Don't create StatisticsRecorder in the single process mode.
   scoped_ptr<base::StatisticsRecorder> statistics;
   if (!base::StatisticsRecorder::IsActive()) {
     statistics.reset(new base::StatisticsRecorder());
   }
 
-  // Initialize statistical testing infrastructure.
-  base::FieldTrialList field_trial;
+  // Initialize statistical testing infrastructure.  We set client_id to the
+  // empty string to disallow the renderer process from creating its own
+  // one-time randomized trials; they should be created in the browser process.
+  base::FieldTrialList field_trial(EmptyString());
   // Ensure any field trials in browser are reflected into renderer.
   if (parsed_command_line.HasSwitch(switches::kForceFieldTestNameAndValue)) {
     std::string persistent = parsed_command_line.GetSwitchValueASCII(
         switches::kForceFieldTestNameAndValue);
     bool ret = field_trial.CreateTrialsInChildProcess(persistent);
     DCHECK(ret);
   }
 
   // Load pepper plugins before engaging the sandbox.
   PepperPluginRegistry::GetInstance();
@@ skipping 25 matching lines @@
         pool->Recycle();
       TRACE_EVENT_BEGIN_ETW("RendererMain.START_MSG_LOOP", 0, 0);
       MessageLoop::current()->Run();
       TRACE_EVENT_END_ETW("RendererMain.START_MSG_LOOP", 0, 0);
     }
   }
   platform.PlatformUninitialize();
   TRACE_EVENT_END_ETW("RendererMain", 0, "");
   return 0;
 }