[content test_utils] Fix RunAllTasksUntilIdle hang

See crbug.com/1035189 for explanation of issue and fix and why it ever
worked (ish).

R=carlscab@google.com

Bug: 1035189
Change-Id: Id1c5468e631c00ab2ea4de6065bd20a28dc8af0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1972294
Commit-Queue: Gabriel Charette <gab@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Carlos Caballero <carlscab@google.com>
Cr-Commit-Position: refs/heads/master@{#726072}

content/public/test/test_utils.cc

@@ -14,6 +14,7 @@
 #include "base/message_loop/message_loop_current.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/post_task.h"
 #include "base/task/sequence_manager/sequence_manager.h"
@@ -79,6 +80,12 @@ class TaskObserver : public base::TaskObserver {
   void WillProcessTask(const base::PendingTask& pending_task,
                        bool was_blocked_or_low_priority) override {}
   void DidProcessTask(const base::PendingTask& pending_task) override {
+    if (base::EndsWith(pending_task.posted_from.file_name(), "base/run_loop.cc",
+                       base::CompareCase::SENSITIVE)) {
+      // Don't consider RunLoop internal tasks (i.e. QuitClosure() reposted by
+      // ProxyToTaskRunner() or RunLoop timeouts) as actual work.
+      return;
+    }
     processed_ = true;
   }
 
@@ -148,9 +155,15 @@ void RunAllTasksUntilIdle() {
     TaskObserver task_observer;
     base::MessageLoopCurrent::Get()->AddTaskObserver(&task_observer);
 
-    base::RunLoop run_loop;
+    // This must use RunLoop::Type::kNestableTasksAllowed in case this
+    // RunAllTasksUntilIdle() call is nested inside an existing Run(). Without
+    // it, the QuitWhenIdleClosure() below would never run if it's posted from
+    // another thread (i.e.. by run_loop.cc's ProxyToTaskRunner).
+    base::RunLoop run_loop(base::RunLoop::Type::kNestableTasksAllowed);
+
     base::ThreadPoolInstance::Get()->FlushAsyncForTesting(
         run_loop.QuitWhenIdleClosure());
+
     run_loop.Run();
 
     base::MessageLoopCurrent::Get()->RemoveTaskObserver(&task_observer);

content/public/test/test_utils_unittest.cc

+// Copyright 2019 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 "content/public/test/test_utils.h"
+
+#include "base/run_loop.h"
+#include "base/task/post_task.h"
+#include "base/test/bind_test_util.h"
+#include "base/test/task_environment.h"
+#include "base/threading/platform_thread.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+// Regression test for crbug.com/1035189.
+TEST(ContentTestUtils, NestedRunAllTasksUntilIdleWithPendingThreadPoolWork) {
+  base::test::TaskEnvironment task_environment;
+
+  bool thread_pool_task_completed = false;
+  base::PostTask(
+      FROM_HERE, {base::ThreadPool()}, base::BindLambdaForTesting([&]() {
+        base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(200));
+        thread_pool_task_completed = true;
+      }));
+
+  base::RunLoop run_loop;
+
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::BindLambdaForTesting([&]() {
+        // Nested RunAllTasksUntilIdle() (i.e. crbug.com/1035189).
+        content::RunAllTasksUntilIdle();
+        EXPECT_TRUE(thread_pool_task_completed);
+        run_loop.Quit();
+      }));
+
+  run_loop.Run();
+  EXPECT_TRUE(thread_pool_task_completed);
+}

content/test/BUILD.gn

@@ -1851,6 +1851,7 @@ test("content_unittests") {
     "../public/test/no_renderer_crashes_assertion_unittest.cc",
     "../public/test/permission_type_unittest.cc",
     "../public/test/referrer_unittest.cc",
+    "../public/test/test_utils_unittest.cc",
     "../renderer/categorized_worker_pool_unittest.cc",
     "../renderer/child_frame_compositing_helper_unittest.cc",
     "../renderer/compositor/layer_tree_view_unittest.cc",