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..8db4acb24a1e9facbd25e63f89a4fdf46faa8ca1 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"
@@ -729,6 +732,33 @@ class ContentMainRunnerImpl : public ContentMainRunner {
     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);