cc: Handle future timebases properly in DelayBasedTimeSource

cc/scheduler/delay_based_time_source_unittest.cc

Index: cc/scheduler/delay_based_time_source_unittest.cc
diff --git a/cc/scheduler/delay_based_time_source_unittest.cc b/cc/scheduler/delay_based_time_source_unittest.cc
index ac54f57a6344ab89287372c4c1527dfbb4a36f40..b018dc369c67a250d4ddf222d89f16ec132856b0 100644
--- a/cc/scheduler/delay_based_time_source_unittest.cc
+++ b/cc/scheduler/delay_based_time_source_unittest.cc
@@ -305,6 +305,115 @@ TEST(DelayBasedTimeSource, HanldlesSignificantIntervalChangesImmediately) {
   EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
 }
 
+TEST(DelayBasedTimeSource, JitteryRuntimeWithFutureTimebases) {
+  scoped_refptr<base::TestSimpleTaskRunner> task_runner =
+      new base::TestSimpleTaskRunner;
+  FakeTimeSourceClient client;
+  scoped_refptr<FakeDelayBasedTimeSource> timer =
+      FakeDelayBasedTimeSource::Create(Interval(), task_runner.get());
+  timer->SetClient(&client);
+  timer->SetActive(true);
+
+  // Run the first tick.
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  base::TimeTicks future_timebase = timer->Now() + Interval() * 10;
+
+  // 1ms jitter
+  base::TimeDelta jitter1 = base::TimeDelta::FromMilliseconds(1);
+
+  // Tick with +1ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() + jitter1);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(15, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with 0ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() - jitter1);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with -1ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() - jitter1);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(17, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with 0ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() + jitter1);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // 8 ms jitter
+  base::TimeDelta jitter8 = base::TimeDelta::FromMilliseconds(8);
+
+  // Tick with +8ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() + jitter8);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(8, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with 0ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() - jitter8);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with -8ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() - jitter8);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(24, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with 0ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() + jitter8);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // 15 ms jitter
+  base::TimeDelta jitter15  = base::TimeDelta::FromMilliseconds(15);
+
+  // Tick with +15ms jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() + jitter15);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(1, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with 0ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() - jitter15);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with -15ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() - jitter15);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(31, task_runner->NextPendingTaskDelay().InMilliseconds());
+
+  // Tick with 0ms of jitter
+  future_timebase += Interval();
+  timer->SetTimebaseAndInterval(future_timebase, Interval());
+  timer->SetNow(timer->Now() + Interval() + jitter15);
+  task_runner->RunPendingTasks();
+  EXPECT_EQ(16, task_runner->NextPendingTaskDelay().InMilliseconds());
+}
+
 TEST(DelayBasedTimeSourceTest, AchievesTargetRateWithNoNoise) {
   int num_iterations = 10;