Return main thread scroll layer in FindScrollLayerForDeviceViewportPoint

cc/trees/layer_tree_host_impl_unittest.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 446 matching lines @@
   }
 
   void pinch_zoom_pan_viewport_forces_commit_redraw(float device_scale_factor);
   void pinch_zoom_pan_viewport_test(float device_scale_factor);
   void pinch_zoom_pan_viewport_and_scroll_test(float device_scale_factor);
   void pinch_zoom_pan_viewport_and_scroll_boundary_test(
       float device_scale_factor);
 
   void SetupMouseMoveAtWithDeviceScale(float device_scale_factor);
 
+  void SetupMouseMoveAtTestScrollbarStates(bool main_thread_scrolling);
+
   scoped_refptr<AnimationTimeline> timeline() { return timeline_; }
 
  protected:
   virtual std::unique_ptr<CompositorFrameSink> CreateCompositorFrameSink() {
     return FakeCompositorFrameSink::Create3d();
   }
 
   void DrawOneFrame() {
     LayerTreeHostImpl::FrameData frame_data;
     host_impl_->PrepareToDraw(&frame_data);
@@ skipping 11137 matching lines @@
       FakeCompositorFrameSink::Create3d(TestWebGraphicsContext3D::Create());
   host_impl_->InitializeRenderer(gpu_raster_compositor_frame_sink.get());
   EXPECT_TRUE(host_impl_->use_gpu_rasterization());
 
   // Re-initialize with a software output surface.
   compositor_frame_sink_ = FakeCompositorFrameSink::CreateSoftware();
   host_impl_->InitializeRenderer(compositor_frame_sink_.get());
   EXPECT_FALSE(host_impl_->use_gpu_rasterization());
 }
 
-TEST_F(LayerTreeHostImplTest, LayerTreeHostImplTestScrollbarStates) {
+void LayerTreeHostImplTest::SetupMouseMoveAtTestScrollbarStates(

[bokan, 2017/01/13 19:23:38]

IMO, TestScrollbarStates would be a better name

+    bool main_thread_scrolling) {
   LayerTreeSettings settings = DefaultSettings();
   settings.scrollbar_fade_delay = base::TimeDelta::FromMilliseconds(500);
   settings.scrollbar_fade_duration = base::TimeDelta::FromMilliseconds(300);
   settings.scrollbar_animator = LayerTreeSettings::THINNING;
 
   gfx::Size viewport_size(300, 200);
   gfx::Size content_size(1000, 1000);
   gfx::Size child_layer_size(250, 150);
   gfx::Size scrollbar_size_1(gfx::Size(15, viewport_size.height()));
   gfx::Size scrollbar_size_2(gfx::Size(15, child_layer_size.height()));
 
   const int scrollbar_1_id = 10;
   const int scrollbar_2_id = 11;
   const int child_clip_id = 12;
   const int child_scroll_id = 13;
 
   CreateHostImpl(settings, CreateCompositorFrameSink());
   host_impl_->active_tree()->SetDeviceScaleFactor(1);
   host_impl_->SetViewportSize(viewport_size);
   CreateScrollAndContentsLayers(host_impl_->active_tree(), content_size);
   host_impl_->active_tree()->InnerViewportContainerLayer()->SetBounds(
       viewport_size);
   LayerImpl* root_scroll =
       host_impl_->active_tree()->OuterViewportScrollLayer();
 
+  if (main_thread_scrolling) {
+    root_scroll->set_main_thread_scrolling_reasons(

[chaopeng, 2017/01/13 19:15:28]

Can child layer be not main thread scroll if the parent has
main_thread_scrolling_reasons?

[bokan, 2017/01/13 19:23:38]

Yes, they're independent so a child that scrolls on impl can have a parent that
scrolls on main. A child that scrolls on main can have a parent that scrolls on
impl.

That said, in this case I'd also make the child main thread scroll.

+        MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects);
+  }
+
   // scrollbar_1 on root scroll.
   std::unique_ptr<SolidColorScrollbarLayerImpl> scrollbar_1 =
       SolidColorScrollbarLayerImpl::Create(host_impl_->active_tree(),
                                            scrollbar_1_id, VERTICAL, 5, 5, true,
                                            true);
   scrollbar_1->SetScrollLayerId(root_scroll->id());
   scrollbar_1->SetDrawsContent(true);
   scrollbar_1->SetBounds(scrollbar_size_1);
   scrollbar_1->SetTouchEventHandlerRegion(gfx::Rect(scrollbar_size_1));
   host_impl_->active_tree()
@@ skipping 79 matching lines @@
   EXPECT_FALSE(scrollbar_1_animation_controller->mouse_is_over_scrollbar());
   EXPECT_FALSE(scrollbar_2_animation_controller->mouse_is_near_scrollbar());
   EXPECT_FALSE(scrollbar_2_animation_controller->mouse_is_over_scrollbar());
   host_impl_->MouseMoveAt(gfx::Point(10, 150));
   EXPECT_TRUE(scrollbar_1_animation_controller->mouse_is_near_scrollbar());
   EXPECT_TRUE(scrollbar_1_animation_controller->mouse_is_over_scrollbar());
   EXPECT_FALSE(scrollbar_2_animation_controller->mouse_is_near_scrollbar());
   EXPECT_FALSE(scrollbar_2_animation_controller->mouse_is_over_scrollbar());
 }
 
+TEST_F(LayerTreeHostImplTest,
+       LayerTreeHostImplTestScrollbarStatesInMainThreadScorlling) {
+  SetupMouseMoveAtTestScrollbarStates(true);
+}
+
+TEST_F(LayerTreeHostImplTest,
+       LayerTreeHostImplTestScrollbarStatesInNotMainThreadScorlling) {
+  SetupMouseMoveAtTestScrollbarStates(false);
+}
+
 }  // namespace
 }  // namespace cc