Refactor unreliable hit test code to avoid owning_layers

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index a82de31691a1547c794c37727430cdb39160baa1..c431b868efa526430ed845990c275bfe1e88b9b7 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -1018,6 +1018,59 @@ TEST_F(LayerTreeHostImplTest, ScrollWithOverlappingNonScrollableLayer) {
   EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD, status.thread);
 }
 
+TEST_F(LayerTreeHostImplTest, ScrolledOverlappingDrawnScrollbarLayer) {
+  LayerTreeImpl* layer_tree_impl = host_impl_->active_tree();
+  gfx::Size content_size = gfx::Size(360, 600);
+  gfx::Size scroll_content_size = gfx::Size(345, 3800);
+  gfx::Size scrollbar_size = gfx::Size(15, 600);
+
+  host_impl_->SetViewportSize(content_size);
+  std::unique_ptr<LayerImpl> root = LayerImpl::Create(layer_tree_impl, 1);
+  root->SetBounds(content_size);
+  root->SetPosition(gfx::PointF());
+
+  std::unique_ptr<LayerImpl> clip = LayerImpl::Create(layer_tree_impl, 2);
+  clip->SetBounds(content_size);
+  clip->SetPosition(gfx::PointF());
+
+  std::unique_ptr<LayerImpl> scroll = LayerImpl::Create(layer_tree_impl, 3);
+  scroll->SetBounds(scroll_content_size);
+  scroll->SetScrollClipLayer(clip->id());
+  scroll->SetDrawsContent(true);
+
+  std::unique_ptr<SolidColorScrollbarLayerImpl> drawnScrollbar =

[ajuma, 2017/02/28 00:38:58]

drawn_scrollbar

[pdr., 2017/02/28 01:01:36]

third_party/WebKitten spotted! :D

Done

+      SolidColorScrollbarLayerImpl::Create(layer_tree_impl, 4, VERTICAL, 10, 0,
+                                           false, true);
+  drawnScrollbar->SetBounds(scrollbar_size);
+  drawnScrollbar->SetPosition(gfx::PointF(345, 0));
+  drawnScrollbar->SetScrollLayerId(scroll->id());
+  drawnScrollbar->SetDrawsContent(true);
+  drawnScrollbar->test_properties()->opacity = 1.f;
+
+  std::unique_ptr<LayerImpl> squash = LayerImpl::Create(layer_tree_impl, 5);
+  squash->SetBounds(gfx::Size(140, 300));
+  squash->SetPosition(gfx::PointF(220, 0));
+  squash->SetDrawsContent(true);
+
+  scroll->test_properties()->AddChild(std::move(drawnScrollbar));
+  scroll->test_properties()->AddChild(std::move(squash));
+  clip->test_properties()->AddChild(std::move(scroll));
+  root->test_properties()->AddChild(std::move(clip));
+
+  layer_tree_impl->SetRootLayerForTesting(std::move(root));
+  layer_tree_impl->BuildPropertyTreesForTesting();
+  layer_tree_impl->DidBecomeActive();
+
+  // The point hits squash layer and also scrollbar layer, but because the
+  // scrollbar layer is not an ancestor of squash, we cannot scroll on the impl

[ajuma, 2017/02/28 00:38:58]

Just to clarify, would things change at all if scrollbar layer were an ancestor,
or is it just that it's a non-scrollable scrollbar?

[pdr., 2017/02/28 01:01:36]

This comment was incorrectly cribbed from
ScrollWithOverlappingNonScrollableLayer. Updated with your suggestion.

+  // thread.
+  auto status = host_impl_->ScrollBegin(BeginState(gfx::Point(350, 150)).get(),
+                                        InputHandler::WHEEL);
+  EXPECT_EQ(InputHandler::SCROLL_UNKNOWN, status.thread);
+  EXPECT_EQ(MainThreadScrollingReason::kFailedHitTest,
+            status.main_thread_scrolling_reasons);
+}
+
 TEST_F(LayerTreeHostImplTest, NonFastScrollableRegionBasic) {
   SetupScrollAndContentsLayers(gfx::Size(200, 200));
   host_impl_->SetViewportSize(gfx::Size(100, 100));