Desktop fast shutdown experiment

Set up an experiment to see the impact of always using the fast exit
path. For context, see https://groups.google.com/a/chromium.org/d/topic/chromium-dev/AMB2Y7Sqj48/discussion

Testing: launch with --enable-features=DesktopFastShutdown

BUG=653647

Review-Url: https://codereview.chromium.org/2528173003
Cr-Commit-Position: refs/heads/master@{#436328}

chrome/browser/BUILD.gn

@@ -384,6 +384,8 @@ split_static_library("browser") {
     "favicon/favicon_utils.h",
     "favicon/large_icon_service_factory.cc",
     "favicon/large_icon_service_factory.h",
+    "features.cc",
+    "features.h",
     "file_select_helper.cc",
     "file_select_helper.h",
     "file_select_helper_mac.mm",

chrome/browser/chrome_browser_field_trials_desktop.cc

@@ -14,6 +14,7 @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
+#include "chrome/browser/features.h"
 #include "chrome/browser/prerender/prerender_field_trial.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
@@ -112,6 +113,12 @@ void SetupDesktopFieldTrials(const base::CommandLine& parsed_command_line) {
 #if defined(OS_WIN)
   SetupStabilityDebugging();
 #endif  // defined(OS_WIN)
+  // Activate the experiment as early as possible to increase its visibility
+  // (e.g. the likelihood of its presence in the serialized system profile).
+  // This also needs to happen before the browser rendez-vous attempt
+  // (NotifyOtherProcessOrCreate) in PreMainMessageLoopRun so the corresponding
+  // metrics are tagged.
+  base::FeatureList::IsEnabled(features::kDesktopFastShutdown);
 }
 
 }  // namespace chrome

chrome/browser/chrome_browser_main.cc

@@ -176,7 +176,9 @@
 #include "chrome/browser/metrics/thread_watcher_android.h"
 #include "ui/base/resource/resource_bundle_android.h"
 #else
+#include "chrome/browser/features.h"
 #include "chrome/browser/feedback/feedback_profile_observer.h"
+#include "chrome/browser/lifetime/application_lifetime.h"
 #endif  // defined(OS_ANDROID)
 
 #if defined(OS_LINUX) && !defined(OS_CHROMEOS)
@@ -1982,6 +1984,12 @@ bool ChromeBrowserMainParts::MainMessageLoopRun(int* result_code) {
       g_browser_process->local_state());
   run_loop.Run();
 
+  if (base::FeatureList::IsEnabled(features::kDesktopFastShutdown)) {
+    // Experiment to determine the impact of always taking the quick exit path.
+    // There is no returning from this call as it terminates the process.
+    chrome::SessionEnding();
+  }
+
   return true;
 #endif  // defined(OS_ANDROID)
 }

chrome/browser/features.cc

+// Copyright 2016 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 "chrome/browser/features.h"
+
+namespace features {
+
+const base::Feature kDesktopFastShutdown{"DesktopFastShutdown",
+                                         base::FEATURE_DISABLED_BY_DEFAULT};
+
+}  // namespace features

chrome/browser/features.h

+// Copyright 2016 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.
+
+// Contains features that need inclusion from multiple files. Features used from
+// a single .cc file should be declared in the file's anonymous namespace.
+
+#ifndef CHROME_BROWSER_FEATURES_H_
+#define CHROME_BROWSER_FEATURES_H_
+
+#include "base/feature_list.h"
+
+namespace features {
+
+extern const base::Feature kDesktopFastShutdown;
+
+}  // namespace features
+
+#endif  // CHROME_BROWSER_FEATURES_H_