[base] Enable FileDescriptorWatcher under IO_MOCK_TIME too

R=fdoray@chromium.org

Bug: 708584
Change-Id: I3d51b3e1b567974805d255cc1300d1b0baf49ebb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594914
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656474}

base/test/scoped_task_environment.cc

@@ -416,7 +416,8 @@ void ScopedTaskEnvironment::InitializeThreadPool() {
 
 void ScopedTaskEnvironment::CompleteInitialization() {
 #if defined(OS_POSIX) || defined(OS_FUCHSIA)
-  if (main_thread_type() == MainThreadType::IO) {
+  if (main_thread_type() == MainThreadType::IO ||
+      main_thread_type() == MainThreadType::IO_MOCK_TIME) {
     file_descriptor_watcher_ =
         std::make_unique<FileDescriptorWatcher>(GetMainThreadTaskRunner());
   }

base/test/scoped_task_environment_unittest.cc

@@ -287,8 +287,7 @@ TEST_P(ScopedTaskEnvironmentTest, SingleThreadShouldNotInitializeThreadPool) {
 #if defined(OS_POSIX)
 TEST_F(ScopedTaskEnvironmentTest, SupportsFileDescriptorWatcherOnIOMainThread) {
   ScopedTaskEnvironment scoped_task_environment(
-      ScopedTaskEnvironment::MainThreadType::IO,
-      ScopedTaskEnvironment::ThreadPoolExecutionMode::ASYNC);
+      ScopedTaskEnvironment::MainThreadType::IO);
 
   int pipe_fds_[2];
   ASSERT_EQ(0, pipe(pipe_fds_));
@@ -302,6 +301,32 @@ TEST_F(ScopedTaskEnvironmentTest, SupportsFileDescriptorWatcherOnIOMainThread) {
   // This will hang if the notification doesn't occur as expected.
   run_loop.Run();
 }
+
+TEST_F(ScopedTaskEnvironmentTest,
+       SupportsFileDescriptorWatcherOnIOMockTimeMainThread) {
+  ScopedTaskEnvironment scoped_task_environment(
+      ScopedTaskEnvironment::MainThreadType::IO_MOCK_TIME);
+
+  int pipe_fds_[2];
+  ASSERT_EQ(0, pipe(pipe_fds_));
+
+  RunLoop run_loop;
+
+  ThreadTaskRunnerHandle::Get()->PostDelayedTask(
+      FROM_HERE, BindLambdaForTesting([&]() {
+        int64_t x = 1;
+        auto ret = write(pipe_fds_[1], &x, sizeof(x));
+        ASSERT_EQ(static_cast<size_t>(ret), sizeof(x));
+      }),
+      TimeDelta::FromHours(1));
+
+  auto controller = FileDescriptorWatcher::WatchReadable(
+      pipe_fds_[0], run_loop.QuitClosure());
+
+  // This will hang if the notification doesn't occur as expected (Run() should
+  // fast-forward-time when idle).
+  run_loop.Run();
+}
 #endif  // defined(OS_POSIX)
 
 // Verify that the TickClock returned by