Initial implementation for sharing field trial state (win)

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 01bb5f00f42ce6a9499708f7a53c5766054c62fc..18939da1c8f2c193525d30982a7332ed92acd15c 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -26,12 +26,14 @@
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
+#include "base/memory/shared_memory.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.h"
 #include "base/process/process_handle.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/string_number_conversions.h"
@@ -146,12 +148,34 @@ void InitializeFieldTrialAndFeatureList(
 
   // Ensure any field trials in browser are reflected into the child
   // process.
+  #if defined(OS_WIN)
+  if (command_line.HasSwitch("field_trial_handle")) {
+    int field_trial_handle = std::stoi(
+      command_line.GetSwitchValueASCII("field_trial_handle"));
+    size_t field_trial_length = std::stoi(
+      command_line.GetSwitchValueASCII("field_trial_length"));

[Alexei Svitkine (slow), 2016/10/03 15:28:05]

I suggest using a single flag whose value is the pair of these. Please define
this flag name in a *_switches.cc/.h file like we do for other flags. It can go
in content_switches.cc. I think.

[lawrencewu, 2016/10/03 21:36:11]

Done.

+
+    HANDLE handle = reinterpret_cast<HANDLE>(field_trial_handle);
+    base::SharedMemoryHandle shm_handle = base::SharedMemoryHandle(
+      handle, base::GetCurrentProcId());
+
+    base::SharedMemory shared_memory(shm_handle, false);
+    shared_memory.Map(field_trial_length);
+
+    char *field_trial_state = static_cast<char*>(shared_memory.memory());
+    bool result = base::FieldTrialList::CreateTrialsFromString(
+      std::string(field_trial_state),

[Alexei Svitkine (slow), 2016/10/03 15:28:05]

When wrapping indent 4, not 2. You can possibly just run "git cl format" to
automatically fix this.

[lawrencewu, 2016/10/03 21:36:11]

Done. git cl format++

+      std::set<std::string>());
+    DCHECK(result);
+  }
+  #else

[Alexei Svitkine (slow), 2016/10/03 15:28:05]

Nit: ifdefs shouldn't be indented.

[lawrencewu, 2016/10/03 21:36:11]

Done.

   if (command_line.HasSwitch(switches::kForceFieldTrials)) {
     bool result = base::FieldTrialList::CreateTrialsFromString(
-        command_line.GetSwitchValueASCII(switches::kForceFieldTrials),
-        std::set<std::string>());
+      command_line.GetSwitchValueASCII(switches::kForceFieldTrials),
+      std::set<std::string>());
     DCHECK(result);
   }
+  #endif
 
   std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
   feature_list->InitializeFromCommandLine(