Enable FeatureList for the GPU process.

content/app/content_main_runner.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 "content/public/app/content_main_runner.h"
 
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <memory>
 #include <string>
 #include <utility>
 
 #include "base/allocator/allocator_check.h"
 #include "base/allocator/allocator_extension.h"
 #include "base/at_exit.h"
+#include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/debug/debugger.h"
 #include "base/debug/stack_trace.h"
+#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/i18n/icu_util.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/process/launch.h"
 #include "base/process/memory.h"
 #include "base/process/process_handle.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ skipping 81 matching lines @@
 #endif
 extern int RendererMain(const content::MainFunctionParams&);
 extern int UtilityMain(const MainFunctionParams&);
 #if defined(OS_ANDROID)
 extern int DownloadMain(const MainFunctionParams&);
 #endif
 }  // namespace content
 
 namespace content {
 
+namespace {
+
+// This sets up two singletons responsible for managing field trials. The
+// |field_trial_list| singleton lives on the stack and must outlive the Run()
+// method of the process.
+void InitializeFieldTrialAndFeatureList(
+    std::unique_ptr<base::FieldTrialList>* field_trial_list) {
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+  std::string process_type =
+      command_line.GetSwitchValueASCII(switches::kProcessType);
+
+  // Initialize statistical testing infrastructure.  We set the entropy
+  // provider to nullptr to disallow non-browser processes from creating
+  // their own one-time randomized trials; they should be created in the
+  // browser process.
+  field_trial_list->reset(new base::FieldTrialList(nullptr));
+
+  // Ensure any field trials in browser are reflected into the child
+  // process.
+  if (command_line.HasSwitch(switches::kForceFieldTrials)) {
+    bool result = base::FieldTrialList::CreateTrialsFromString(
+        command_line.GetSwitchValueASCII(switches::kForceFieldTrials),
+        std::set<std::string>());
+    DCHECK(result);
+  }
+
+  std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
+  feature_list->InitializeFromCommandLine(
+      command_line.GetSwitchValueASCII(switches::kEnableFeatures),
+      command_line.GetSwitchValueASCII(switches::kDisableFeatures));
+  base::FeatureList::SetInstance(std::move(feature_list));
+}
+
+}  // namespace
+
 #if !defined(CHROME_MULTIPLE_DLL_CHILD)
 base::LazyInstance<ContentBrowserClient>
     g_empty_content_browser_client = LAZY_INSTANCE_INITIALIZER;
 #endif  //  !CHROME_MULTIPLE_DLL_CHILD
 
 #if !defined(CHROME_MULTIPLE_DLL_BROWSER)
 base::LazyInstance<ContentGpuClient>
     g_empty_content_gpu_client = LAZY_INSTANCE_INITIALIZER;
 base::LazyInstance<ContentRendererClient>
     g_empty_content_renderer_client = LAZY_INSTANCE_INITIALIZER;
@@ skipping 156 matching lines @@
   // line so update it here with the new version.
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
   std::string process_type =
       command_line.GetSwitchValueASCII(switches::kProcessType);
   ContentClientInitializer::Set(process_type, delegate);
 
   MainFunctionParams main_params(command_line);
   main_params.zygote_child = true;
 
+  std::unique_ptr<base::FieldTrialList> field_trial_list;
+  InitializeFieldTrialAndFeatureList(&field_trial_list);
+
   for (size_t i = 0; i < arraysize(kMainFunctions); ++i) {
     if (process_type == kMainFunctions[i].name)
       return kMainFunctions[i].function(main_params);
   }
 
   if (delegate)
     return delegate->RunProcess(process_type, main_params);
 
   NOTREACHED() << "Unknown zygote process type: " << process_type;
   return 1;
@@ skipping 408 matching lines @@
   }
 
   int Run() override {
     DCHECK(is_initialized_);
     DCHECK(!is_shutdown_);
     const base::CommandLine& command_line =
         *base::CommandLine::ForCurrentProcess();
     std::string process_type =
         command_line.GetSwitchValueASCII(switches::kProcessType);
 
+    // Run this logic on all child processes. Zygotes will run this at a later
+    // point in time when the command line has been updated.
+    std::unique_ptr<base::FieldTrialList> field_trial_list;
+    if (process_type != "" && process_type != switches::kZygoteProcess)

[jam, 2016/05/03 21:33:48]

nit !process_type.empty() which is convention

[erikchen, 2016/05/03 21:49:32]

Done.

+      InitializeFieldTrialAndFeatureList(&field_trial_list);
+
     base::HistogramBase::EnableActivityReportHistogram(process_type);
 
     MainFunctionParams main_params(command_line);
     main_params.ui_task = ui_task_;
 #if defined(OS_WIN)
     main_params.sandbox_info = &sandbox_info_;
 #elif defined(OS_MACOSX)
     main_params.autorelease_pool = autorelease_pool_.get();
 #endif
 
@@ skipping 56 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(ContentMainRunnerImpl);
 };
 
 // static
 ContentMainRunner* ContentMainRunner::Create() {
   return new ContentMainRunnerImpl();
 }
 
 }  // namespace content