Enable FeatureList for the GPU process.

content/common/child_process_host_impl.cc

Index: content/common/child_process_host_impl.cc
diff --git a/content/common/child_process_host_impl.cc b/content/common/child_process_host_impl.cc
index e9b81e75f9d894f99bc530a4fbe79bf8c9609dff..b3268b0cb2a00ea559b0c32ef6004ffa4c18bd5e 100644
--- a/content/common/child_process_host_impl.cc
+++ b/content/common/child_process_host_impl.cc
@@ -7,11 +7,14 @@
 #include <limits>
 
 #include "base/atomic_sequence_num.h"
+#include "base/base_switches.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/hash.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/numerics/safe_math.h"
 #include "base/path_service.h"
@@ -198,6 +201,28 @@ int ChildProcessHostImpl::GenerateChildProcessUniqueId() {
   return id;
 }
 
+void ChildProcessHostImpl::CopyEnableDisableFeatureFlags(

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

Nit: CopyFeatureAndFieldTrialFlags() since now this also doing
field_trial_states.

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

Done.

+    base::CommandLine* cmd_line) {
+  std::string enabled_features;
+  std::string disabled_features;
+  base::FeatureList::GetInstance()->GetFeatureOverrides(&enabled_features,
+                                                        &disabled_features);
+  if (!enabled_features.empty())
+    cmd_line->AppendSwitchASCII(switches::kEnableFeatures, enabled_features);
+  if (!disabled_features.empty())
+    cmd_line->AppendSwitchASCII(switches::kDisableFeatures, disabled_features);
+
+  // If we run base::FieldTrials, we want to pass to their state to the
+  // child process so that it can act in accordance with each state, or record
+  // histograms relating to the base::FieldTrial states.

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

Nit: I'd remove the ", or record histograms relating to the base::FieldTrial
states." part of the sentence. I think this was referring to the old
field-trial-suffixed histograms which we don't use anymore.

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

Done.

+  std::string field_trial_states;
+  base::FieldTrialList::AllStatesToString(&field_trial_states);
+  if (!field_trial_states.empty()) {
+    cmd_line->AppendSwitchASCII(switches::kForceFieldTrials,
+                                field_trial_states);
+  }
+}
+
 uint64_t ChildProcessHostImpl::ChildProcessUniqueIdToTracingProcessId(
     int child_process_id) {
   // In single process mode, all the children are hosted in the same process,