Optimize for TouchStart responsiveness

components/scheduler/renderer/renderer_scheduler_impl_unittest.cc

Index: components/scheduler/renderer/renderer_scheduler_impl_unittest.cc
diff --git a/components/scheduler/renderer/renderer_scheduler_impl_unittest.cc b/components/scheduler/renderer/renderer_scheduler_impl_unittest.cc
index c651486d18c9315d3783c1992daac11d200eeaa6..e286f0a3d8dbb11d70aecc55489b40a8be924f47 100644
--- a/components/scheduler/renderer/renderer_scheduler_impl_unittest.cc
+++ b/components/scheduler/renderer/renderer_scheduler_impl_unittest.cc
@@ -126,15 +126,28 @@ void PostingYieldingTestTask(RendererSchedulerImpl* scheduler,
   *should_yield_after = scheduler->ShouldYieldForHighPriorityWork();
 }
 
+enum class SimulateInputType { None, TouchStart, TouchEnd };
+
 void AnticipationTestTask(RendererSchedulerImpl* scheduler,
-                          bool simulate_input,
+                          SimulateInputType simulate_input,
                           bool* is_anticipated_before,
                           bool* is_anticipated_after) {
   *is_anticipated_before = scheduler->IsHighPriorityWorkAnticipated();
-  if (simulate_input) {
-    scheduler->DidHandleInputEventOnCompositorThread(
-        FakeInputEvent(blink::WebInputEvent::GestureFlingStart),
-        RendererScheduler::InputEventState::EVENT_CONSUMED_BY_COMPOSITOR);
+  switch (simulate_input) {
+    case SimulateInputType::None:
+      break;
+
+    case SimulateInputType::TouchStart:
+      scheduler->DidHandleInputEventOnCompositorThread(
+          FakeInputEvent(blink::WebInputEvent::TouchStart),
+          RendererScheduler::InputEventState::EVENT_CONSUMED_BY_COMPOSITOR);
+      break;
+
+    case SimulateInputType::TouchEnd:
+      scheduler->DidHandleInputEventOnCompositorThread(
+          FakeInputEvent(blink::WebInputEvent::TouchEnd),
+          RendererScheduler::InputEventState::EVENT_CONSUMED_BY_COMPOSITOR);
+      break;
   }
   *is_anticipated_after = scheduler->IsHighPriorityWorkAnticipated();
 }
@@ -145,8 +158,6 @@ class RendererSchedulerImplForTest : public RendererSchedulerImpl {
  public:
   using RendererSchedulerImpl::OnIdlePeriodEnded;
   using RendererSchedulerImpl::OnIdlePeriodStarted;
-  using RendererSchedulerImpl::Policy;
-  using RendererSchedulerImpl::PolicyToString;
 
   RendererSchedulerImplForTest(
       scoped_refptr<SchedulerTaskRunnerDelegate> main_task_runner)
@@ -155,6 +166,14 @@ class RendererSchedulerImplForTest : public RendererSchedulerImpl {
   void UpdatePolicyLocked(UpdateType update_type) override {
     update_policy_count_++;
     RendererSchedulerImpl::UpdatePolicyLocked(update_type);
+
+    std::string use_case =
+        RendererScheduler::UseCaseToString(MainThreadOnly().current_use_case);
+    if (MainThreadOnly().touchstart_expected_soon) {
+      use_cases_.push_back(use_case + " scroll expected");
+    } else {
+      use_cases_.push_back(use_case);
+    }
   }
 
   void EnsureUrgentPolicyUpdatePostedOnMainThread() {
@@ -169,21 +188,22 @@ class RendererSchedulerImplForTest : public RendererSchedulerImpl {
 
   bool BeginMainFrameOnCriticalPath() {
     base::AutoLock lock(any_thread_lock_);
-    return AnyThread().begin_main_frame_on_critical_path_;
+    return AnyThread().begin_main_frame_on_critical_path;
   }
 
   int update_policy_count_;
+  std::vector<std::string> use_cases_;
 };
 
 // Lets gtest print human readable Policy values.
 ::std::ostream& operator<<(::std::ostream& os,
-                           const RendererSchedulerImplForTest::Policy& policy) {
-  return os << RendererSchedulerImplForTest::PolicyToString(policy);
+                           const RendererScheduler::UseCase& use_case) {
+  return os << RendererScheduler::UseCaseToString(use_case);
 }
 
 class RendererSchedulerImplTest : public testing::Test {
  public:
-  using Policy = RendererSchedulerImpl::Policy;
+  using UseCase = RendererSchedulerImpl::UseCase;
 
   RendererSchedulerImplTest() : clock_(new base::SimpleTestTickClock()) {
     clock_->Advance(base::TimeDelta::FromMicroseconds(5000));
@@ -255,10 +275,27 @@ class RendererSchedulerImplTest : public testing::Test {
     scheduler_->DidCommitFrameToCompositor();
   }
 
+  void ForceMainthreadScrollingUseCase() {
+    cc::BeginFrameArgs begin_frame_args = cc::BeginFrameArgs::Create(
+        BEGINFRAME_FROM_HERE, clock_->NowTicks(), base::TimeTicks(),
+        base::TimeDelta::FromMilliseconds(1000), cc::BeginFrameArgs::NORMAL);
+    begin_frame_args.on_critical_path = true;
+    scheduler_->WillBeginFrame(begin_frame_args);
+  }
+
   void EnableIdleTasks() { DoMainFrame(); }
 
-  Policy CurrentPolicy() {
-    return scheduler_->MainThreadOnly().current_policy_;
+  UseCase CurrentUseCase() {
+    return scheduler_->MainThreadOnly().current_use_case;
+  }
+
+  UseCase ForceUpdatePolicyAndGetCurrentUseCase() {
+    scheduler_->ForceUpdatePolicy();
+    return scheduler_->MainThreadOnly().current_use_case;
+  }
+
+  bool TouchStartExpectedSoon() {
+    return scheduler_->MainThreadOnly().touchstart_expected_soon;
   }
 
   // Helper for posting several tasks of specific types. |task_descriptor| is a
@@ -306,7 +343,12 @@ class RendererSchedulerImplTest : public testing::Test {
  protected:
   static base::TimeDelta priority_escalation_after_input_duration() {
     return base::TimeDelta::FromMilliseconds(
-        RendererSchedulerImpl::kPriorityEscalationAfterInputMillis);
+        UserModel::kPriorityEscalationAfterInputMillis);
+  }
+
+  static base::TimeDelta subsequent_input_expected_after_input_duration() {
+    return base::TimeDelta::FromMilliseconds(
+        UserModel::kExpectSubsequentInputMillis);
   }
 
   static base::TimeDelta maximum_idle_period_duration() {
@@ -334,11 +376,11 @@ class RendererSchedulerImplTest : public testing::Test {
     }
   }
 
-  static void CheckAllPolicyToString() {
-    CallForEachEnumValue<RendererSchedulerImpl::Policy>(
-        RendererSchedulerImpl::Policy::FIRST_POLICY,
-        RendererSchedulerImpl::Policy::POLICY_COUNT,
-        &RendererSchedulerImpl::PolicyToString);
+  static void CheckAllUseCaseToString() {
+    CallForEachEnumValue<RendererSchedulerImpl::UseCase>(
+        RendererSchedulerImpl::UseCase::FIRST_USE_CASE,
+        RendererSchedulerImpl::UseCase::USE_CASE_COUNT,
+        &RendererSchedulerImpl::UseCaseToString);
   }
 
   scoped_ptr<base::SimpleTestTickClock> clock_;
@@ -637,9 +679,12 @@ TEST_F(
   PostTestTasks(&run_order, "C1 T1");
 
   scheduler_->DidAnimateForInputOnCompositorThread();
-  scheduler_->WillBeginFrame(cc::BeginFrameArgs::Create(
+  cc::BeginFrameArgs begin_frame_args1 = cc::BeginFrameArgs::Create(
       BEGINFRAME_FROM_HERE, clock_->NowTicks(), base::TimeTicks(),
-      base::TimeDelta::FromMilliseconds(16), cc::BeginFrameArgs::NORMAL));
+      base::TimeDelta::FromMilliseconds(1000), cc::BeginFrameArgs::NORMAL);
+  begin_frame_args1.on_critical_path = true;
+  scheduler_->WillBeginFrame(begin_frame_args1);
+  scheduler_->DidCommitFrameToCompositor();  // Starts Idle Period
   RunUntilIdle();
 
   EXPECT_THAT(run_order, testing::ElementsAre(std::string("C1")));
@@ -793,28 +838,32 @@ TEST_F(RendererSchedulerImplTest, TestTouchstartPolicy_MainThread) {
 
 TEST_F(RendererSchedulerImplTest, LoadingPriorityPolicy) {
   std::vector<std::string> run_order;
-  PostTestTasks(&run_order, "L1 I1 D1 C1 D2 C2");
+  PostTestTasks(&run_order, "I1 D1 C1 T1 L1 D2 C2 T2 L2");
 
   scheduler_->OnPageLoadStarted();
   EnableIdleTasks();
   RunUntilIdle();
-  // In loading policy compositor tasks are best effort and should be run last.
-  EXPECT_THAT(run_order,
-              testing::ElementsAre(std::string("L1"), std::string("D1"),
-                                   std::string("D2"), std::string("I1"),
-                                   std::string("C1"), std::string("C2")));
+
+  // In loading policy, loading tasks are prioritized other others.
+  std::string loading_policy_expected[] = {
+      std::string("L1"), std::string("L2"), std::string("D1"),
+      std::string("C1"), std::string("T1"), std::string("D2"),
+      std::string("C2"), std::string("T2"), std::string("I1")};
+  EXPECT_THAT(run_order, testing::ElementsAreArray(loading_policy_expected));
 
   // Advance 1.5s and try again, the loading policy should have ended and the
-  // task order should return to normal.
+  // task order should return to the NONE use case where loading tasks
+  // are prioritized.
   clock_->Advance(base::TimeDelta::FromMilliseconds(1500));
   run_order.clear();
-  PostTestTasks(&run_order, "L1 I1 D1 C1 D2 C2");
+  PostTestTasks(&run_order, "I1 D1 C1 T1 L1 D2 C2 T2 L2");
   EnableIdleTasks();
   RunUntilIdle();
-  EXPECT_THAT(run_order,
-              testing::ElementsAre(std::string("L1"), std::string("D1"),
-                                   std::string("C1"), std::string("D2"),
-                                   std::string("C2"), std::string("I1")));
+  std::string default_order_expected[] = {
+      std::string("L1"), std::string("L2"), std::string("D1"),
+      std::string("C1"), std::string("T1"), std::string("D2"),
+      std::string("C2"), std::string("T2"), std::string("I1")};
+  EXPECT_THAT(run_order, testing::ElementsAreArray(default_order_expected));
 }
 
 TEST_F(RendererSchedulerImplTest,
@@ -962,7 +1011,9 @@ TEST_F(RendererSchedulerImplTest,
 }
 
 TEST_F(RendererSchedulerImplTest,
-       TestCompositorPolicyDoesNotStarveDefaultTasks) {
+       TestMainthreadScrollingUseCaseDoesNotStarveDefaultTasks) {
+  ForceMainthreadScrollingUseCase();
+
   std::vector<std::string> run_order;
   PostTestTasks(&run_order, "D1 C1");
 
@@ -984,52 +1035,28 @@ TEST_F(RendererSchedulerImplTest,
 
 TEST_F(RendererSchedulerImplTest,
        TestCompositorPolicyEnds_CompositorHandlesInput) {
-  std::vector<std::string> run_order;
-  PostTestTasks(&run_order, "D1 C1 D2 C2");
-
   scheduler_->DidHandleInputEventOnCompositorThread(
       FakeInputEvent(blink::WebInputEvent::GestureFlingStart),
       RendererScheduler::InputEventState::EVENT_CONSUMED_BY_COMPOSITOR);
-  RunUntilIdle();
-  EXPECT_THAT(run_order,
-              testing::ElementsAre(std::string("C1"), std::string("C2"),
-                                   std::string("D1"), std::string("D2")));
+  EXPECT_EQ(UseCase::COMPOSITOR_GESTURE,
+            ForceUpdatePolicyAndGetCurrentUseCase());
 
-  run_order.clear();
   clock_->Advance(base::TimeDelta::FromMilliseconds(1000));
-  PostTestTasks(&run_order, "D1 C1 D2 C2");
-
-  // Compositor policy mode should have ended now that the clock has advanced.
-  RunUntilIdle();
-  EXPECT_THAT(run_order,
-              testing::ElementsAre(std::string("D1"), std::string("C1"),
-                                   std::string("D2"), std::string("C2")));
+  EXPECT_EQ(UseCase::NONE, ForceUpdatePolicyAndGetCurrentUseCase());
 }
 
 TEST_F(RendererSchedulerImplTest,
        TestCompositorPolicyEnds_MainThreadHandlesInput) {
-  std::vector<std::string> run_order;
-  PostTestTasks(&run_order, "D1 C1 D2 C2");
-
   scheduler_->DidHandleInputEventOnCompositorThread(
       FakeInputEvent(blink::WebInputEvent::GestureFlingStart),
       RendererScheduler::InputEventState::EVENT_FORWARDED_TO_MAIN_THREAD);
   scheduler_->DidHandleInputEventOnMainThread(
       FakeInputEvent(blink::WebInputEvent::GestureFlingStart));
-  RunUntilIdle();
-  EXPECT_THAT(run_order,
-              testing::ElementsAre(std::string("C1"), std::string("C2"),
-                                   std::string("D1"), std::string("D2")));
+  EXPECT_EQ(UseCase::COMPOSITOR_GESTURE,
+            ForceUpdatePolicyAndGetCurrentUseCase());
 
-  run_order.clear();
   clock_->Advance(base::TimeDelta::FromMilliseconds(1000));
-  PostTestTasks(&run_order, "D1 C1 D2 C2");
-
-  // Compositor policy mode should have ended now that the clock has advanced.
-  RunUntilIdle();
-  EXPECT_THAT(run_order,
-              testing::ElementsAre(std::string("D1"), std::string("C1"),
-                                   std::string("D2"), std::string("C2")));
+  EXPECT_EQ(UseCase::NONE, ForceUpdatePolicyAndGetCurrentUseCase());
 }
 
 TEST_F(RendererSchedulerImplTest, TestTouchstartPolicyEndsAfterTimeout) {
@@ -1093,22 +1120,25 @@ TEST_F(RendererSchedulerImplTest, TestIsHighPriorityWorkAnticipated) {
   bool is_anticipated_before = false;
   bool is_anticipated_after = false;
 
-  bool simulate_input = false;
   default_task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&AnticipationTestTask, scheduler_.get(), simulate_input,
-                 &is_anticipated_before, &is_anticipated_after));
+      FROM_HERE, base::Bind(&AnticipationTestTask, scheduler_.get(),
+                            SimulateInputType::None, &is_anticipated_before,
+                            &is_anticipated_after));
   RunUntilIdle();
   // In its default state, without input receipt, the scheduler should indicate
   // that no high-priority is anticipated.
   EXPECT_FALSE(is_anticipated_before);
   EXPECT_FALSE(is_anticipated_after);
 
-  simulate_input = true;
   default_task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&AnticipationTestTask, scheduler_.get(), simulate_input,
-                 &is_anticipated_before, &is_anticipated_after));
+      FROM_HERE, base::Bind(&AnticipationTestTask, scheduler_.get(),
+                            SimulateInputType::TouchStart,
+                            &is_anticipated_before, &is_anticipated_after));
+  bool dummy;
+  default_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&AnticipationTestTask, scheduler_.get(),
+                            SimulateInputType::TouchEnd, &dummy, &dummy));
+
   RunUntilIdle();
   // When input is received, the scheduler should indicate that high-priority
   // work is anticipated.
@@ -1116,14 +1146,29 @@ TEST_F(RendererSchedulerImplTest, TestIsHighPriorityWorkAnticipated) {
   EXPECT_TRUE(is_anticipated_after);
 
   clock_->Advance(priority_escalation_after_input_duration() * 2);
-  simulate_input = false;
   default_task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&AnticipationTestTask, scheduler_.get(), simulate_input,
-                 &is_anticipated_before, &is_anticipated_after));
-  RunUntilIdle();
-  // Without additional input, the scheduler should indicate that high-priority
-  // work is no longer anticipated.
+      FROM_HERE, base::Bind(&AnticipationTestTask, scheduler_.get(),
+                            SimulateInputType::None, &is_anticipated_before,
+                            &is_anticipated_after));
+  RunUntilIdle();
+  // Without additional input, the scheduler should go into NONE
+  // use case but with scrolling expected where high-priority work is still
+  // anticipated.
+  EXPECT_EQ(UseCase::NONE, CurrentUseCase());
+  EXPECT_TRUE(TouchStartExpectedSoon());
+  EXPECT_TRUE(is_anticipated_before);
+  EXPECT_TRUE(is_anticipated_after);
+
+  clock_->Advance(subsequent_input_expected_after_input_duration() * 2);
+  default_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&AnticipationTestTask, scheduler_.get(),
+                            SimulateInputType::None, &is_anticipated_before,
+                            &is_anticipated_after));
+  RunUntilIdle();
+  // Eventually the scheduler should go into the default use case where
+  // high-priority work is no longer anticipated.
+  EXPECT_EQ(UseCase::NONE, CurrentUseCase());
+  EXPECT_FALSE(TouchStartExpectedSoon());
   EXPECT_FALSE(is_anticipated_before);
   EXPECT_FALSE(is_anticipated_after);
 }
@@ -1132,6 +1177,8 @@ TEST_F(RendererSchedulerImplTest, TestShouldYield) {
   bool should_yield_before = false;
   bool should_yield_after = false;
 
+  ForceMainthreadScrollingUseCase();
+
   default_task_runner_->PostTask(
       FROM_HERE, base::Bind(&PostingYieldingTestTask, scheduler_.get(),
                             default_task_runner_, false, &should_yield_before,
@@ -1146,7 +1193,7 @@ TEST_F(RendererSchedulerImplTest, TestShouldYield) {
                             compositor_task_runner_, false,
                             &should_yield_before, &should_yield_after));
   RunUntilIdle();
-  // Posting while not in compositor priority shouldn't cause yielding.
+  // Posting while not mainthread scrolling shouldn't cause yielding.
   EXPECT_FALSE(should_yield_before);
   EXPECT_FALSE(should_yield_after);
 
@@ -1158,7 +1205,9 @@ TEST_F(RendererSchedulerImplTest, TestShouldYield) {
   // We should be able to switch to compositor priority mid-task.
   EXPECT_FALSE(should_yield_before);
   EXPECT_TRUE(should_yield_after);
+}
 
+TEST_F(RendererSchedulerImplTest, TestShouldYield_TouchStart) {
   // Receiving a touchstart should immediately trigger yielding, even if
   // there's no immediately pending work in the compositor queue.
   EXPECT_FALSE(scheduler_->ShouldYieldForHighPriorityWork());
@@ -1170,14 +1219,14 @@ TEST_F(RendererSchedulerImplTest, TestShouldYield) {
 }
 
 TEST_F(RendererSchedulerImplTest, SlowMainThreadInputEvent) {
-  EXPECT_EQ(Policy::NORMAL, CurrentPolicy());
+  EXPECT_EQ(UseCase::NONE, CurrentUseCase());
 
   // An input event should bump us into input priority.
   scheduler_->DidHandleInputEventOnCompositorThread(
       FakeInputEvent(blink::WebInputEvent::GestureFlingStart),
       RendererScheduler::InputEventState::EVENT_FORWARDED_TO_MAIN_THREAD);
   RunUntilIdle();
-  EXPECT_EQ(Policy::COMPOSITOR_PRIORITY, CurrentPolicy());
+  EXPECT_EQ(UseCase::COMPOSITOR_GESTURE, CurrentUseCase());
 
   // Simulate the input event being queued for a very long time. The compositor
   // task we post here represents the enqueued input task.
@@ -1188,12 +1237,12 @@ TEST_F(RendererSchedulerImplTest, SlowMainThreadInputEvent) {
 
   // Even though we exceeded the input priority escalation period, we should
   // still be in compositor priority since the input remains queued.
-  EXPECT_EQ(Policy::COMPOSITOR_PRIORITY, CurrentPolicy());
+  EXPECT_EQ(UseCase::COMPOSITOR_GESTURE, CurrentUseCase());
 
   // After the escalation period ends we should go back into normal mode.
   clock_->Advance(priority_escalation_after_input_duration() * 2);
   RunUntilIdle();
-  EXPECT_EQ(Policy::NORMAL, CurrentPolicy());
+  EXPECT_EQ(UseCase::NONE, CurrentUseCase());
 }
 
 class RendererSchedulerImplWithMockSchedulerTest
@@ -1396,10 +1445,14 @@ TEST_F(RendererSchedulerImplWithMockSchedulerTest,
 
   EXPECT_EQ(1, mock_scheduler_->update_policy_count_);
 
-  RunUntilIdle();
   // We expect both the urgent and the delayed updates to run in addition to the
-  // earlier updated cause by IsHighPriorityWorkAnticipated.
-  EXPECT_EQ(3, mock_scheduler_->update_policy_count_);
+  // earlier updated cause by IsHighPriorityWorkAnticipated, a final update
+  // transitions from 'not_scrolling scroll expected' to 'not_scrolling'.
+  RunUntilIdle();
+  EXPECT_THAT(mock_scheduler_->use_cases_,
+              testing::ElementsAre(
+                  std::string("touchstart"), std::string("touchstart"),
+                  std::string("none scroll expected"), std::string("none")));
 }
 
 class RendererSchedulerImplWithMessageLoopTest
@@ -1754,8 +1807,8 @@ TEST_F(RendererSchedulerImplTest, MultipleSuspendsNeedMultipleResumes) {
               testing::ElementsAre(std::string("T1"), std::string("T2")));
 }
 
-TEST_F(RendererSchedulerImplTest, PolicyToString) {
-  CheckAllPolicyToString();
+TEST_F(RendererSchedulerImplTest, UseCaseToString) {
+  CheckAllUseCaseToString();
 }
 
 TEST_F(RendererSchedulerImplTest, MismatchedDidHandleInputEventOnMainThread) {