Create TaskScheduler in BrowserMainLoop constructor.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index 5021cd5c45c38f59493fbb778338da8fff3082a0..924a2d254e530095a20d5468579e891a40cc34f4 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -532,6 +532,8 @@ BrowserMainLoop::BrowserMainLoop(const MainFunctionParams& parameters)
            tracing::TraceConfigFile::GetInstance()->GetStartupDuration() > 0)) {
   DCHECK(!g_current_browser_main_loop);
   g_current_browser_main_loop = this;
+
+  base::TaskScheduler::Create("");

[robliao, 2017/04/24 18:15:54]

Should we be more aggressive about the creation point now? Maybe
browser_main_runner is the place to be?

[gab, 2017/04/25 15:29:15]

Agreed for ASAP but this is essentially the same logical point: BrowserMainLoop
is called from BrowserMainRunnerImpl::Initialize() and BrowserMain() invokes
BrowserMainRunner::Create() and BrowserMainRunnerImpl::Initialize() in a row @
https://cs.chromium.org/chromium/src/content/browser/browser_main.cc?rcl=76b4...

So since this boils down to pretty much as early as possible in both cases, I'd
say here is better since it's what manages threads and pools.

[robliao, 2017/04/25 17:21:30]

I think this change is fine for now, but given that we will be removing the
browser threads management portion long term, it may make more sense to abstract
that outside of BrowserMainLoop when we arrive at that point.

 }
 

[robliao, 2017/04/25 17:21:30]

Document the use of "".

 BrowserMainLoop::~BrowserMainLoop() {
@@ -952,14 +954,15 @@ void BrowserMainLoop::CreateStartupTasks() {
 int BrowserMainLoop::CreateThreads() {
   TRACE_EVENT0("startup,rail", "BrowserMainLoop::CreateThreads");
 
-  auto task_scheduler_init_params =
-      GetContentClient()->browser()->GetTaskSchedulerInitParams();
-  if (!task_scheduler_init_params)
-    task_scheduler_init_params = GetDefaultTaskSchedulerInitParams();
-  DCHECK(task_scheduler_init_params);
-
-  base::TaskScheduler::CreateAndSetDefaultTaskScheduler(
-      "", *task_scheduler_init_params.get());
+  {
+    auto task_scheduler_init_params =
+        GetContentClient()->browser()->GetTaskSchedulerInitParams();
+    if (!task_scheduler_init_params)
+      task_scheduler_init_params = GetDefaultTaskSchedulerInitParams();
+    DCHECK(task_scheduler_init_params);
+    base::TaskScheduler::GetInstance()->Start(
+        *task_scheduler_init_params.get());
+  }
 
   GetContentClient()->browser()->PerformExperimentalTaskSchedulerRedirections();