Pref service: enable for user prefs in chrome behind a flag.

chrome/browser/browser_process_impl.cc

Index: chrome/browser/browser_process_impl.cc
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index 5ec7f984898a06b53aa354c26d737117ecc37c54..76b826212098a2bd79cdf3587202211df227bdcf 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -76,6 +76,7 @@
 #include "chrome/browser/update_client/chrome_update_query_params_delegate.h"
 #include "chrome/common/channel_info.h"
 #include "chrome/common/chrome_constants.h"
+#include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/crash_keys.h"
@@ -194,7 +195,8 @@ static const int kUpdateCheckIntervalHours = 6;
 // and Windows. We have a timeout here because we're unable to run the UI
 // messageloop and there's some deadlock risk. Our only option is to exit
 // anyway.
-static const int kEndSessionTimeoutSeconds = 10;
+static constexpr base::TimeDelta kEndSessionTimeout =
+    base::TimeDelta::FromSeconds(10);
 #endif
 
 using content::BrowserThread;
@@ -467,12 +469,22 @@ void BrowserProcessImpl::EndSession() {
   ProfileManager* pm = profile_manager();
   std::vector<Profile*> profiles(pm->GetLoadedProfiles());
   scoped_refptr<RundownTaskCounter> rundown_counter(new RundownTaskCounter());
+  const bool pref_service_enabled =
+      base::FeatureList::IsEnabled(features::kPrefService);
+  std::vector<scoped_refptr<base::SequencedTaskRunner>> profile_writer_runners;
   for (size_t i = 0; i < profiles.size(); ++i) {
     Profile* profile = profiles[i];
     profile->SetExitType(Profile::EXIT_SESSION_ENDED);
     if (profile->GetPrefs()) {
       profile->GetPrefs()->CommitPendingWrite();
-      rundown_counter->Post(profile->GetIOTaskRunner().get());
+      if (pref_service_enabled) {
+        rundown_counter->Post(content::BrowserThread::GetTaskRunnerForThread(
+                                  content::BrowserThread::IO)
+                                  .get());
+        profile_writer_runners.push_back(profile->GetIOTaskRunner());
+      } else {
+        rundown_counter->Post(profile->GetIOTaskRunner().get());
+      }
     }
   }
 
@@ -513,8 +525,16 @@ void BrowserProcessImpl::EndSession() {
   // GPU process synchronously. Because the system may not be allowing
   // processes to launch, this can result in a hang. See
   // http://crbug.com/318527.
-  rundown_counter->TimedWait(
-      base::TimeDelta::FromSeconds(kEndSessionTimeoutSeconds));
+  base::Time start = base::Time::Now();

[sky, 2017/03/15 15:19:17]

Use timeticks?

[Sam McNally, 2017/03/16 06:58:22]

Done.

+  if (rundown_counter->TimedWait(kEndSessionTimeout) && pref_service_enabled) {

[sky, 2017/03/15 15:19:17]

What does a return value of true mean for TimedWait (It doesn't document what it
means, and should).

[Sam McNally, 2017/03/16 06:58:22]

It returns whether everything finished before the timeout. Documented it and
extracted a variable with a name that should make it clearer why the code here
cares.

+    scoped_refptr<RundownTaskCounter> profile_write_rundown_counter(
+        new RundownTaskCounter());
+    for (auto& profile_writer_runner : profile_writer_runners) {

[sky, 2017/03/15 15:19:17]

no {}

[Sam McNally, 2017/03/16 06:58:22]

Done.

+      profile_write_rundown_counter->Post(profile_writer_runner.get());
+    }
+    profile_write_rundown_counter->TimedWait(kEndSessionTimeout -

[sky, 2017/03/15 15:19:17]

Does RundownTaskCounter deal with potentially negative time deltas?

[Sam McNally, 2017/03/16 06:58:22]

I think it should, but I've changed it to take an end time instead to avoid the
unnecessary subtraction here. End times in the past are also valid.

+                                             (base::Time::Now() - start));
+  }
 #else
   NOTIMPLEMENTED();
 #endif