Reland RedirectNonUINonIOBrowserThreads to TaskScheduler by default on trunk

This reverts commit f07732ec
(https://codereview.chromium.org/2791933004)
and reapplies b6d0c9a0
(https://codereview.chromium.org/2690183002/).

BUG=653916, 707986
TBR=jam@chromium.org, rkaplow@chromium.org
Previously reviewed at https://codereview.chromium.org/2690183002/

Review-Url: https://codereview.chromium.org/2856583002
Cr-Commit-Position: refs/heads/master@{#468376}

base/threading/thread_restrictions.h

@@ -34,9 +34,11 @@ class Predictor;
 namespace content {
 class BrowserGpuChannelHostFactory;
 class BrowserGpuMemoryBufferManager;
+class BrowserMainLoop;
 class BrowserShutdownProfileDumper;
 class BrowserSurfaceViewManager;
 class BrowserTestBase;
+class CategorizedWorkerPool;
 class NestedMessagePumpAndroid;
 class ScopedAllowWaitForAndroidLayoutTests;
 class ScopedAllowWaitForDebugURL;
@@ -45,7 +47,6 @@ class SynchronousCompositor;
 class SynchronousCompositorBrowserFilter;
 class SynchronousCompositorHost;
 class TextInputClientMac;
-class CategorizedWorkerPool;
 }  // namespace content
 namespace dbus {
 class Bus;
@@ -185,6 +186,7 @@ class BASE_EXPORT ThreadRestrictions {
   friend class android_webview::AwFormDatabaseService;
   friend class android_webview::CookieManager;
   friend class base::StackSamplingProfiler;
+  friend class content::BrowserMainLoop;
   friend class content::BrowserShutdownProfileDumper;
   friend class content::BrowserSurfaceViewManager;
   friend class content::BrowserTestBase;

content/browser/browser_main_loop.cc

@@ -1259,86 +1259,88 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
   service_manager_context_.reset();
   mojo_ipc_support_.reset();
 
-  // Must be size_t so we can subtract from it.
-  for (size_t thread_id = BrowserThread::ID_COUNT - 1;
-       thread_id >= (BrowserThread::UI + 1);
-       --thread_id) {
-    // Find the thread object we want to stop. Looping over all valid
-    // BrowserThread IDs and DCHECKing on a missing case in the switch
-    // statement helps avoid a mismatch between this code and the
-    // BrowserThread::ID enumeration.
-    //
-    // The destruction order is the reverse order of occurrence in the
-    // BrowserThread::ID list. The rationale for the order is as
-    // follows (need to be filled in a bit):
-    //
-    //
-    // - The IO thread is the only user of the CACHE thread.
-    //
-    // - The PROCESS_LAUNCHER thread must be stopped after IO in case
-    //   the IO thread posted a task to terminate a process on the
-    //   process launcher thread.
-    //
-    // - (Not sure why DB stops last.)
-    switch (thread_id) {
-      case BrowserThread::DB: {
-        TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:DBThread");
-        ResetThread_DB(std::move(db_thread_));
-        break;
-      }
-      case BrowserThread::FILE: {
-        TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:FileThread");
-        // Clean up state that lives on or uses the FILE thread before it goes
-        // away.
-        save_file_manager_->Shutdown();
-        ResetThread_FILE(std::move(file_thread_));
-        break;
-      }
-      case BrowserThread::FILE_USER_BLOCKING: {
-        TRACE_EVENT0("shutdown",
-                      "BrowserMainLoop::Subsystem:FileUserBlockingThread");
-        ResetThread_FILE_USER_BLOCKING(std::move(file_user_blocking_thread_));
-        break;
-      }
-      case BrowserThread::PROCESS_LAUNCHER: {
-        TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:LauncherThread");
-        ResetThread_PROCESS_LAUNCHER(std::move(process_launcher_thread_));
-        break;
-      }
-      case BrowserThread::CACHE: {
-        TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:CacheThread");
-        ResetThread_CACHE(std::move(cache_thread_));
-        break;
-      }
-      case BrowserThread::IO: {
-        TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:IOThread");
-        ResetThread_IO(std::move(io_thread_));
-        break;
+  {
+    base::ThreadRestrictions::ScopedAllowWait allow_wait_for_join;
+
+    // Must be size_t so we can subtract from it.
+    for (size_t thread_id = BrowserThread::ID_COUNT - 1;
+         thread_id >= (BrowserThread::UI + 1); --thread_id) {
+      // Find the thread object we want to stop. Looping over all valid
+      // BrowserThread IDs and DCHECKing on a missing case in the switch
+      // statement helps avoid a mismatch between this code and the
+      // BrowserThread::ID enumeration.
+      //
+      // The destruction order is the reverse order of occurrence in the
+      // BrowserThread::ID list. The rationale for the order is as follows (need
+      // to be filled in a bit):
+      //
+      // - The IO thread is the only user of the CACHE thread.
+      //
+      // - The PROCESS_LAUNCHER thread must be stopped after IO in case
+      //   the IO thread posted a task to terminate a process on the
+      //   process launcher thread.
+      //
+      // - (Not sure why DB stops last.)
+      switch (thread_id) {
+        case BrowserThread::DB: {
+          TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:DBThread");
+          ResetThread_DB(std::move(db_thread_));
+          break;
+        }
+        case BrowserThread::FILE: {
+          TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:FileThread");
+          // Clean up state that lives on or uses the FILE thread before it goes
+          // away.
+          save_file_manager_->Shutdown();
+          ResetThread_FILE(std::move(file_thread_));
+          break;
+        }
+        case BrowserThread::FILE_USER_BLOCKING: {
+          TRACE_EVENT0("shutdown",
+                       "BrowserMainLoop::Subsystem:FileUserBlockingThread");
+          ResetThread_FILE_USER_BLOCKING(std::move(file_user_blocking_thread_));
+          break;
+        }
+        case BrowserThread::PROCESS_LAUNCHER: {
+          TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:LauncherThread");
+          ResetThread_PROCESS_LAUNCHER(std::move(process_launcher_thread_));
+          break;
+        }
+        case BrowserThread::CACHE: {
+          TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:CacheThread");
+          ResetThread_CACHE(std::move(cache_thread_));
+          break;
+        }
+        case BrowserThread::IO: {
+          TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:IOThread");
+          ResetThread_IO(std::move(io_thread_));
+          break;
+        }
+        case BrowserThread::UI:
+        case BrowserThread::ID_COUNT:
+          NOTREACHED();
+          break;
       }
-      case BrowserThread::UI:
-      case BrowserThread::ID_COUNT:
-        NOTREACHED();
-        break;
     }
-  }
-  {
-    TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:IndexedDBThread");
-    ResetThread_IndexedDb(std::move(indexed_db_thread_));
-  }
+    {
+      TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:IndexedDBThread");
+      ResetThread_IndexedDb(std::move(indexed_db_thread_));
+    }
 
-  // Close the blocking I/O pool after the other threads. Other threads such
-  // as the I/O thread may need to schedule work like closing files or flushing
-  // data during shutdown, so the blocking pool needs to be available. There
-  // may also be slow operations pending that will blcok shutdown, so closing
-  // it here (which will block until required operations are complete) gives
-  // more head start for those operations to finish.
-  {
-    TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:ThreadPool");
-    BrowserThreadImpl::ShutdownThreadPool();
-  }
-  {
-    TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:TaskScheduler");
-    base::TaskScheduler::GetInstance()->Shutdown();
+    // Close the blocking I/O pool after the other threads. Other threads such
+    // as the I/O thread may need to schedule work like closing files or
+    // flushing data during shutdown, so the blocking pool needs to be
+    // available. There may also be slow operations pending that will blcok
+    // shutdown, so closing it here (which will block until required operations
+    // are complete) gives more head start for those operations to finish.
+    {
+      TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:ThreadPool");
+      BrowserThreadImpl::ShutdownThreadPool();
+    }
+    {
+      TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:TaskScheduler");
+      base::TaskScheduler::GetInstance()->Shutdown();
+    }
   }
 
   // Must happen after the IO thread is shutdown since this may be accessed from

testing/variations/fieldtrial_testing_config.json

@@ -365,6 +365,7 @@
                 {
                     "name": "Default",
                     "params": {
+                        "RedirectNonUINonIOBrowserThreads": "true",
                         "RedirectSequencedWorkerPools": "true"
                     }
                 },