Expose ScopedTaskEnvironment::DescribePendingMainThreadTasks()

Used while debugging
https://chromium-review.googlesource.com/c/chromium/src/+/1635473
and I think it'll be a nice general purpose debugging tool for
developers.

R=alexclarke@chromium.org

Bug: 946657
Change-Id: I479eb51d00b835bf8a4a75a1b044ab5db12aae13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1639389Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Auto-Submit: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665879}

base/test/scoped_task_environment.cc

@@ -645,6 +645,10 @@ bool ScopedTaskEnvironment::NextTaskIsDelayed() const {
   return !delay.is_zero() && !delay.is_max();
 }
 
+void ScopedTaskEnvironment::DescribePendingMainThreadTasks() const {
+  LOG(INFO) << sequence_manager_->DescribeAllPendingTasks();
+}
+
 ScopedTaskEnvironment::TestTaskTracker::TestTaskTracker()
     : internal::ThreadPoolImpl::TaskTrackerImpl("ScopedTaskEnvironment"),
       can_run_tasks_cv_(&lock_),

base/test/scoped_task_environment.h

@@ -227,9 +227,10 @@ class ScopedTaskEnvironment {
   // Returns the current virtual tick time (initially starting at 0).
   base::TimeTicks NowTicks() const;
 
-  // Only valid for instances with a MOCK_TIME MainThreadType.
-  // Returns the number of pending tasks (delayed and non-delayed) of the main
-  // thread's TaskRunner.
+  // Only valid for instances with a MOCK_TIME MainThreadType. Returns the
+  // number of pending tasks (delayed and non-delayed) of the main thread's
+  // TaskRunner. When debugging, you can use DescribePendingMainThreadTasks() to
+  // see what those are.
   size_t GetPendingMainThreadTaskCount() const;
 
   // Only valid for instances with a MOCK_TIME MainThreadType.
@@ -242,6 +243,10 @@ class ScopedTaskEnvironment {
   // is immediate or if there is no next task.
   bool NextTaskIsDelayed() const;
 
+  // For debugging purposes: Dumps information about pending tasks on the main
+  // thread.
+  void DescribePendingMainThreadTasks() const;
+
  protected:
   explicit ScopedTaskEnvironment(ScopedTaskEnvironment&& other);
 

base/test/scoped_task_environment_unittest.cc

@@ -18,6 +18,7 @@
 #include "base/task/thread_pool/thread_pool.h"
 #include "base/test/bind_test_util.h"
 #include "base/test/mock_callback.h"
+#include "base/test/mock_log.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/sequence_local_storage_slot.h"
@@ -43,7 +44,11 @@ namespace test {
 
 namespace {
 
+using ::testing::_;
+using ::testing::HasSubstr;
 using ::testing::IsNull;
+using ::testing::Not;
+using ::testing::Return;
 
 class ScopedTaskEnvironmentForTest : public ScopedTaskEnvironment {
  public:
@@ -572,6 +577,29 @@ TEST_F(ScopedTaskEnvironmentTest, SetsDefaultRunTimeout) {
   EXPECT_EQ(RunLoop::ScopedRunTimeoutForTest::Current(), old_run_timeout);
 }
 
+namespace {}
+
+TEST_F(ScopedTaskEnvironmentTest, DescribePendingMainThreadTasks) {
+  ScopedTaskEnvironment scoped_task_environment;
+  ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE, DoNothing());
+
+  test::MockLog mock_log;
+  mock_log.StartCapturingLogs();
+
+  EXPECT_CALL(mock_log, Log(::logging::LOG_INFO, _, _, _,
+                            HasSubstr("scoped_task_environment_unittest.cc")))
+      .WillOnce(Return(true));
+  scoped_task_environment.DescribePendingMainThreadTasks();
+
+  scoped_task_environment.RunUntilIdle();
+
+  EXPECT_CALL(mock_log,
+              Log(::logging::LOG_INFO, _, _, _,
+                  Not(HasSubstr("scoped_task_environment_unittest.cc"))))
+      .WillOnce(Return(true));
+  scoped_task_environment.DescribePendingMainThreadTasks();
+}
+
 INSTANTIATE_TEST_SUITE_P(
     MainThreadDefault,
     ScopedTaskEnvironmentTest,