Initial implementation for sharing field trial state (win)

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/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"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
 #include "components/tracing/browser/trace_config_file.h"
 #include "components/tracing/common/trace_to_console.h"
 #include "components/tracing/common/tracing_switches.h"
@@ skipping 94 matching lines @@
       *base::CommandLine::ForCurrentProcess();
 
   // Initialize statistical testing infrastructure.  We set the entropy
   // provider to nullptr to disallow non-browser processes from creating
   // their own one-time randomized trials; they should be created in the
   // browser process.
   field_trial_list->reset(new base::FieldTrialList(nullptr));
 
   // 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(
       command_line.GetSwitchValueASCII(switches::kEnableFeatures),
       command_line.GetSwitchValueASCII(switches::kDisableFeatures));
   base::FeatureList::SetInstance(std::move(feature_list));
 }
 
 }  // namespace
 
@@ skipping 677 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(ContentMainRunnerImpl);
 };
 
 // static
 ContentMainRunner* ContentMainRunner::Create() {
   return new ContentMainRunnerImpl();
 }
 
 }  // namespace content