Scroll on main if impl-hit testing isn't guaranteed to be correct

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 0fff5ffc332c261241c2f23a03188c0f65549013..560f8d078bc63c30c50dc9073eeeae137e868b17 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -5951,6 +5951,79 @@ TEST_F(LayerTreeHostImplTest, WheelFlingShouldBubble) {
   }
 }
 
+TEST_F(LayerTreeHostImplTest, ScrollUnknownNotOnAncestorChain) {
+  // If we ray cast a scroller that is not on the first layer's ancestor chain,
+  // we should return ScrollUnknown.
+  gfx::Size content_size(100, 100);
+  SetupScrollAndContentsLayers(content_size);
+
+  int scroll_layer_id = 2;
+  LayerImpl* scroll_layer =
+      host_impl_->active_tree()->LayerById(scroll_layer_id);
+  scroll_layer->SetDrawsContent(true);
+
+  int page_scale_layer_id = 5;
+  LayerImpl* page_scale_layer =
+      host_impl_->active_tree()->LayerById(page_scale_layer_id);
+
+  int occluder_layer_id = 6;
+  scoped_ptr<LayerImpl> occluder_layer =
+      LayerImpl::Create(host_impl_->active_tree(), occluder_layer_id);
+  occluder_layer->SetDrawsContent(true);
+  occluder_layer->SetBounds(content_size);
+  occluder_layer->SetContentBounds(content_size);
+  occluder_layer->SetPosition(gfx::PointF());
+  occluder_layer->SetAnchorPoint(gfx::PointF());
+
+  // The parent of the occluder is *above* the scroller.
+  page_scale_layer->AddChild(occluder_layer.Pass());
+
+  DrawFrame();
+
+  EXPECT_EQ(InputHandler::ScrollUnknown,
+            host_impl_->ScrollBegin(gfx::Point(), InputHandler::Wheel));
+}
+
+TEST_F(LayerTreeHostImplTest, ScrollUnknownScrollAncestorMismatch) {
+  // If we ray cast a scroller this is on the first layer's ancestor chain, but
+  // is not the first scroller we encounter when walking up from the layer, we
+  // should also return ScrollUnknown.
+  gfx::Size content_size(100, 100);
+  SetupScrollAndContentsLayers(content_size);
+
+  int scroll_layer_id = 2;
+  LayerImpl* scroll_layer =
+      host_impl_->active_tree()->LayerById(scroll_layer_id);
+  scroll_layer->SetDrawsContent(true);
+
+  int occluder_layer_id = 6;
+  scoped_ptr<LayerImpl> occluder_layer =
+      LayerImpl::Create(host_impl_->active_tree(), occluder_layer_id);
+  occluder_layer->SetDrawsContent(true);
+  occluder_layer->SetBounds(content_size);
+  occluder_layer->SetContentBounds(content_size);
+  occluder_layer->SetPosition(gfx::PointF());
+  occluder_layer->SetAnchorPoint(gfx::PointF());
+
+  int child_scroll_clip_layer_id = 7;
+  scoped_ptr<LayerImpl> child_scroll_clip =
+      LayerImpl::Create(host_impl_->active_tree(), child_scroll_clip_layer_id);
+
+  int child_scroll_layer_id = 8;
+  scoped_ptr<LayerImpl> child_scroll = CreateScrollableLayer(
+      child_scroll_layer_id, content_size, child_scroll_clip.get());
+
+  child_scroll->SetDrawsContent(false);
+
+  child_scroll->AddChild(occluder_layer.Pass());
+  scroll_layer->AddChild(child_scroll.Pass());
+
+  DrawFrame();
+
+  EXPECT_EQ(InputHandler::ScrollUnknown,
+            host_impl_->ScrollBegin(gfx::Point(), InputHandler::Wheel));
+}
+
 // Make sure LatencyInfo carried by LatencyInfoSwapPromise are passed
 // to CompositorFrameMetadata after SwapBuffers();
 TEST_F(LayerTreeHostImplTest, LatencyInfoPassedToCompositorFrameMetadata) {