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);
 
+    // TODO(asvitkine): This logic should run for all child processes.

[Alexei Svitkine (slow), 2016/04/28 15:23:33]

Thanks! You can add 563705 to the BUG= line of this CL.

[erikchen, 2016/04/29 17:45:04]

Done.

+    if (process_type == switches::kGpuProcess ||
+        process_type == switches::kUtilityProcess ||
+        process_type == switches::kPpapiPluginProcess) {
+      // Initialize statistical testing infrastructure.  We set the entropy
+      // provider to NULL to disallow non-browser processes from creating their
+      // own one-time randomized trials; they should be created in the browser
+      // process.
+      base::FieldTrialList field_trial_list(NULL);

[Alexei Svitkine (slow), 2016/04/28 15:23:33]

This is not correct. The FieldTrialList should stay alive for the duration of
the process.

In this case, if you put it outside of the loop, it should be fine since this
calls RunNamedProcessTypeMain() and so the lifetime of FieldTrialList will
outlive whatever else the process does.

You can make it a unique_ptr above the loop and create the object in the loop.

[erikchen, 2016/04/29 17:45:04]

You keep talking about "the loop". Are you referring to the loop in
RunNamedProcessTypeMain()? I moved the object constructor to line 739, where it
should stay alive until RunNamedProcessTypeMain() returns. I prefer to run that
code as early as possible.

[Alexei Svitkine (slow), 2016/04/29 18:06:31]

Woops, when I said "loop" I meant "if". Sorry for the confusion.

+
+      // Ensure any field trials in browser are reflected into the child
+      // process.
+      if (command_line.HasSwitch(switches::kForceFieldTrials)) {

[Alexei Svitkine (slow), 2016/04/28 15:23:33]

It would be good to check whether we propagate this flag when launching child
processes. Not sure if you've done that already.

[erikchen, 2016/04/29 17:45:04]

We weren't propagating it. I added it to
ChildProcessHostImpl::CopyEnableDisableFeatureFlags.

+        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