Enable FeatureList for the GPU process.

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index abe4f13051c45db0ac11f31e7ef09b59fe3f618b..9bfea2c3d1bb7fbbcc27593d3c7241dbe886c3ec 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -15,15 +15,18 @@
 #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"
@@ -125,6 +128,45 @@ extern int DownloadMain(const MainFunctionParams&);
 
 namespace content {
 
+namespace {

[Alexei Svitkine (slow), 2016/05/03 18:59:47]

Nit: Add an empty line below. You can remove the empty line above it.

[erikchen, 2016/05/03 19:22:31]

Done.

+void InitializeFieldTrialAndFeatureList(

[Alexei Svitkine (slow), 2016/05/03 18:59:47]

Nit: Please add a short comment about what this does.

[erikchen, 2016/05/03 19:22:31]

Done.

+    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);
+
+  // TODO(asvitkine): This logic should run for all child processes.
+  // https://crbug.com/563705.
+  if (process_type == switches::kGpuProcess ||
+#if defined(ENABLE_PLUGINS)
+      process_type == switches::kPpapiPluginProcess ||
+#endif  // ENABLE_PLUGINS
+      process_type == switches::kUtilityProcess) {
+    // 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

[Alexei Svitkine (slow), 2016/05/03 18:59:47]

Nit: Add an empty line above it.

[erikchen, 2016/05/03 19:22:31]

Done.

+
 #if !defined(CHROME_MULTIPLE_DLL_CHILD)
 base::LazyInstance<ContentBrowserClient>
     g_empty_content_browser_client = LAZY_INSTANCE_INITIALIZER;
@@ -301,6 +343,9 @@ int RunZygote(const MainFunctionParams& main_function_params,
   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);
@@ -729,6 +774,9 @@ class ContentMainRunnerImpl : public ContentMainRunner {
     std::string process_type =
         command_line.GetSwitchValueASCII(switches::kProcessType);
 
+    std::unique_ptr<base::FieldTrialList> field_trial_list;
+    InitializeFieldTrialAndFeatureList(&field_trial_list);
+
     base::HistogramBase::EnableActivityReportHistogram(process_type);
 
     MainFunctionParams main_params(command_line);