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 685 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);
 
+    // Initialize statistical testing infrastructure.  We set the entropy
+    // provider to NULL to disallow non-browser processes from creating their

[Alexei Svitkine (slow), 2016/04/29 18:06:32]

Nit: NULL -> null

and NULL -> nullptr below.

[erikchen, 2016/04/29 18:34:38]

Done.

+    // own one-time randomized trials; they should be created in the browser
+    // process.
+    base::FieldTrialList field_trial_list(NULL);

[Alexei Svitkine (slow), 2016/04/29 18:06:32]

How does this interact with:

https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/r...

i.e. It would be incorrect to have two FieldTrialList's active in that case. If
the renderer also runs the code, then we should make this a scoped_ptr and
create it inside the if. (But maybe I'm wrong and renderers don't run this code
path?)

[erikchen, 2016/04/29 18:34:38]

whoops! I had meant to remove that.

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