Record size of scroller that user scrolls

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 c7f6e98bea11c02d78ef280cbe3be69432b196e6..dcca63f0f240ac5578c118f30c50d7f97795bd6b 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -15,6 +15,7 @@
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "base/test/histogram_tester.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/animation/animation_host.h"
 #include "cc/animation/animation_id_provider.h"
@@ -754,6 +755,66 @@ TEST_F(LayerTreeHostImplTest, ScrollDeltaRepeatedScrolls) {
                                  scroll_delta + scroll_delta2));
 }
 
+TEST_F(LayerTreeHostImplTest, ScrollerSizeOfCCScrollingHistogramRecordingTest) {
+  const gfx::Size content_size(800, 600);
+  const gfx::Size viewport_size(500, 500);
+  CreateBasicVirtualViewportLayers(viewport_size, content_size);
+
+  LayerImpl* outer_viewport_scroll_layer =
+      host_impl_->active_tree()->OuterViewportScrollLayer();
+  int id = outer_viewport_scroll_layer->id();
+  std::unique_ptr<LayerImpl> child =
+      LayerImpl::Create(host_impl_->active_tree(), id + 2);
+  std::unique_ptr<LayerImpl> child_clip =
+      LayerImpl::Create(host_impl_->active_tree(), id + 3);
+
+  child_clip->SetBounds(gfx::Size(100, 100));
+
+  child->SetScrollClipLayer(child_clip->id());
+  child->SetElementId(LayerIdToElementIdForTesting(child->id()));
+  child->SetBounds(gfx::Size(100, 400));
+  child->SetPosition(gfx::PointF());
+  child->SetDrawsContent(true);
+
+  child_clip->test_properties()->AddChild(std::move(child));
+  outer_viewport_scroll_layer->test_properties()->AddChild(
+      std::move(child_clip));
+  host_impl_->active_tree()->BuildPropertyTreesForTesting();
+
+  base::HistogramTester histogram_tester;
+
+  // Test touch scroll.
+  InputHandler::ScrollStatus status = host_impl_->ScrollBegin(
+      BeginState(gfx::Point()).get(), InputHandler::TOUCHSCREEN);
+  EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD, status.thread);
+  EXPECT_EQ(MainThreadScrollingReason::kNotScrollingOnMain,
+            status.main_thread_scrolling_reasons);
+  host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2d(0, 10)).get());
+  host_impl_->ScrollEnd(EndState().get());
+
+  histogram_tester.ExpectBucketCount("Event.Scroll.ScrollerSize.OnScroll_Touch",
+                                     10000, 1);
+  histogram_tester.ExpectTotalCount("Event.Scroll.ScrollerSize.OnScroll_Touch",
+                                    1);
+
+  // Scrolling root layer doesn't add to count.
+  host_impl_->ScrollBegin(BeginState(gfx::Point(450, 450)).get(),
+                          InputHandler::TOUCHSCREEN);
+  host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2d(0, 10)).get());
+  host_impl_->ScrollEnd(EndState().get());
+  histogram_tester.ExpectTotalCount("Event.Scroll.ScrollerSize.OnScroll_Touch",
+                                    1);
+
+  // Test wheel scroll.
+  host_impl_->ScrollBegin(BeginState(gfx::Point()).get(), InputHandler::WHEEL);
+  host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2d(0, 10)).get());
+  host_impl_->ScrollEnd(EndState().get());
+  histogram_tester.ExpectBucketCount("Event.Scroll.ScrollerSize.OnScroll_Wheel",
+                                     10000, 1);
+  histogram_tester.ExpectTotalCount("Event.Scroll.ScrollerSize.OnScroll_Wheel",
+                                    1);
+}
+
 TEST_F(LayerTreeHostImplTest, ScrollRootCallsCommitAndRedraw) {
   SetupScrollAndContentsLayers(gfx::Size(100, 100));
   host_impl_->active_tree()->BuildPropertyTreesForTesting();