Enable redirection of SequencedWorkerPool to TaskScheduler in TestBrowserThreadBundle.

content/public/test/test_browser_thread_bundle.cc

Index: content/public/test/test_browser_thread_bundle.cc
diff --git a/content/public/test/test_browser_thread_bundle.cc b/content/public/test/test_browser_thread_bundle.cc
index c0c4b4f5f965834fd74aa3380f01b8318787c612..904ef680d81d2d9738a23d07720b8695432df43d 100644
--- a/content/public/test/test_browser_thread_bundle.cc
+++ b/content/public/test/test_browser_thread_bundle.cc
@@ -9,6 +9,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/scoped_async_task_scheduler.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "content/browser/browser_thread_impl.h"
 #include "content/public/test/test_browser_thread.h"
 
@@ -58,6 +59,9 @@ TestBrowserThreadBundle::~TestBrowserThreadBundle() {
 
   scoped_async_task_scheduler_.reset();
 
+  // Disable redirection of SequencedWorkerPools to TaskScheduler.
+  base::SequencedWorkerPool::EnableForProcess();

[gab, 2017/03/22 16:23:30]

Do we need this? Sounds better to have tasks be redirected in a void and explode
than lazily instantiating a very late SequencedWorkerPool w/ workers.

[fdoray, 2017/04/03 14:57:28]

In TestBrowserThreadBundle::CreateThreads(), we enable redirection of
SequencedWorkerPool to TaskScheduler. It is important to disable this
redirection here to bring back the process to its original state.

Some tests instantiate their own SequencedWorkerPool (e.g.
https://cs.chromium.org/chromium/src/components/update_client/update_client_u...).
Without this, they will try to redirect tasks to a non-existent TaskScheduler
and crash.

[gab, 2017/04/03 16:56:17]

I see expand comment here then, something like:

// Disable redirection of SequencedWorkerPools to TaskScheduler.
// This is required in order to reset global state so that tests following this
one in this process can still manage their own SequencedWorkerPool without using
TestBrowserThreadBundle.

+
   // |message_loop_| needs to explicitly go away before fake threads in order
   // for DestructionObservers hooked to |message_loop_| to be able to invoke
   // BrowserThread::CurrentlyOn() -- ref. ~TestBrowserThread().
@@ -93,6 +97,9 @@ void TestBrowserThreadBundle::CreateThreads() {
   scoped_async_task_scheduler_ =
       base::MakeUnique<base::test::ScopedAsyncTaskScheduler>();
 
+  // Enable redirection of SequencedWorkerPools to TaskScheduler.
+  base::SequencedWorkerPool::EnableWithRedirectionToTaskSchedulerForProcess();
+
   if (options_ & REAL_DB_THREAD) {
     db_thread_.reset(new TestBrowserThread(BrowserThread::DB));
     db_thread_->Start();