Scroll with Layers in views::ScrollView

ui/views/controls/scroll_view_unittest.cc

Index: ui/views/controls/scroll_view_unittest.cc
diff --git a/ui/views/controls/scroll_view_unittest.cc b/ui/views/controls/scroll_view_unittest.cc
index b18ebe7647c0215e468a89c7e0dd23d7372b2940..0db9f7a5decb8e7c053872d8ec30f16b3bbf5765 100644
--- a/ui/views/controls/scroll_view_unittest.cc
+++ b/ui/views/controls/scroll_view_unittest.cc
@@ -5,6 +5,9 @@
 #include "ui/views/controls/scroll_view.h"
 
 #include "base/macros.h"
+#include "base/run_loop.h"
+#include "base/test/test_timeouts.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/scrollbar/base_scroll_bar_thumb.h"
@@ -46,7 +49,15 @@ class ScrollViewTestApi {
     return GetBaseScrollBar(orientation)->thumb_;
   }
 
+  gfx::Point IntegralViewOffset() {
+    return gfx::Point() - gfx::ScrollOffsetToFlooredVector2d(CurrentOffset());
+  }
+
+  gfx::ScrollOffset CurrentOffset() { return scroll_view_->CurrentOffset(); }
+
   View* corner_view() { return scroll_view_->corner_view_; }
+  View* contents_viewport() { return scroll_view_->contents_viewport_; }
+  View* contents_container() { return scroll_view_->contents_container_; }
 
  private:
   ScrollView* scroll_view_;
@@ -115,7 +126,8 @@ ui::MouseEvent TestLeftMouseAt(const gfx::Point& location, ui::EventType type) {
 using test::ScrollViewTestApi;
 
 // Test harness that includes a Widget to help test ui::Event handling.
-class WidgetScrollViewTest : public test::WidgetTest {
+class WidgetScrollViewTest : public test::WidgetTest,
+                             public ui::CompositorObserver {
  public:
   static const int kDefaultHeight = 100;
   static const int kDefaultWidth = 100;
@@ -128,7 +140,8 @@ class WidgetScrollViewTest : public test::WidgetTest {
   }
 
   // Adds a ScrollView with a contents view of the given |size| and does layout.
-  ScrollView* AddScrollViewWithContentSize(const gfx::Size& contents_size) {
+  ScrollView* AddScrollViewWithContentSize(const gfx::Size& contents_size,
+                                           bool commit_layers = true) {
     const gfx::Rect default_bounds(50, 50, kDefaultWidth, kDefaultHeight);
     widget_ = CreateTopLevelFramelessPlatformWidget();
 
@@ -142,19 +155,53 @@ class WidgetScrollViewTest : public test::WidgetTest {
 
     widget_->SetContentsView(scroll_view);
     scroll_view->Layout();
+
+    widget_->GetCompositor()->AddObserver(this);
+
+    // Ensure the Compositor has committed layer changes before attempting to
+    // use them for impl-side scrolling. Note that simply RunUntilIdle() works
+    // when tests are run in isolation, but compositor scheduling can interact
+    // between test runs in the general case.
+    if (commit_layers)
+      WaitForCommit();
     return scroll_view;
   }
 
+  // Wait for a commit to be observed on the compositor.
+  void WaitForCommit() {
+    base::RunLoop run_loop;
+    quit_closure_ = run_loop.QuitClosure();
+    base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
+        FROM_HERE, quit_closure_, TestTimeouts::action_timeout());
+    run_loop.Run();
+    EXPECT_TRUE(quit_closure_.is_null()) << "Timed out waiting for a commit.";
+  }
+
   // testing::Test:
   void TearDown() override {
+    widget_->GetCompositor()->RemoveObserver(this);
     if (widget_)
       widget_->CloseNow();
     WidgetTest::TearDown();
   }
 
  private:
+  // ui::CompositorObserver:
+  void OnCompositingDidCommit(ui::Compositor* compositor) override {
+    quit_closure_.Run();
+    quit_closure_.Reset();
+  }
+  void OnCompositingStarted(ui::Compositor* compositor,
+                            base::TimeTicks start_time) override {}
+  void OnCompositingEnded(ui::Compositor* compositor) override {}
+  void OnCompositingAborted(ui::Compositor* compositor) override {}
+  void OnCompositingLockStateChanged(ui::Compositor* compositor) override {}
+  void OnCompositingShuttingDown(ui::Compositor* compositor) override {}
+
   Widget* widget_ = nullptr;
 
+  base::Closure quit_closure_;
+
 #if defined(OS_MACOSX)
   std::unique_ptr<ui::test::ScopedPreferredScrollerStyle> scroller_style_;
 #endif
@@ -168,11 +215,12 @@ const int WidgetScrollViewTest::kDefaultWidth;
 // Verifies the viewport is sized to fit the available space.
 TEST(ScrollViewTest, ViewportSizedToFit) {
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   View* contents = new View;
   scroll_view.SetContents(contents);
   scroll_view.SetBoundsRect(gfx::Rect(0, 0, 100, 100));
   scroll_view.Layout();
-  EXPECT_EQ("0,0 100x100", contents->parent()->bounds().ToString());
+  EXPECT_EQ("0,0 100x100", test_api.contents_viewport()->bounds().ToString());
 }
 
 // Verifies the scrollbars are added as necessary.
@@ -183,6 +231,7 @@ TEST(ScrollViewTest, ScrollBars) {
 #endif
 
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   View* contents = new View;
   scroll_view.SetContents(contents);
   scroll_view.SetBoundsRect(gfx::Rect(0, 0, 100, 100));
@@ -190,8 +239,9 @@ TEST(ScrollViewTest, ScrollBars) {
   // Size the contents such that vertical scrollbar is needed.
   contents->SetBounds(0, 0, 50, 400);
   scroll_view.Layout();
-  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), contents->parent()->width());
-  EXPECT_EQ(100, contents->parent()->height());
+  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(),
+            test_api.contents_viewport()->width());
+  EXPECT_EQ(100, test_api.contents_viewport()->height());
   CheckScrollbarVisibility(scroll_view, VERTICAL, true);
   CheckScrollbarVisibility(scroll_view, HORIZONTAL, false);
   EXPECT_TRUE(!scroll_view.horizontal_scroll_bar() ||
@@ -202,18 +252,19 @@ TEST(ScrollViewTest, ScrollBars) {
   // Size the contents such that horizontal scrollbar is needed.
   contents->SetBounds(0, 0, 400, 50);
   scroll_view.Layout();
-  EXPECT_EQ(100, contents->parent()->width());
+  EXPECT_EQ(100, test_api.contents_viewport()->width());
   EXPECT_EQ(100 - scroll_view.GetScrollBarHeight(),
-            contents->parent()->height());
+            test_api.contents_viewport()->height());
   CheckScrollbarVisibility(scroll_view, VERTICAL, false);
   CheckScrollbarVisibility(scroll_view, HORIZONTAL, true);
 
   // Both horizontal and vertical.
   contents->SetBounds(0, 0, 300, 400);
   scroll_view.Layout();
-  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), contents->parent()->width());
+  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(),
+            test_api.contents_viewport()->width());
   EXPECT_EQ(100 - scroll_view.GetScrollBarHeight(),
-            contents->parent()->height());
+            test_api.contents_viewport()->height());
   CheckScrollbarVisibility(scroll_view, VERTICAL, true);
   CheckScrollbarVisibility(scroll_view, HORIZONTAL, true);
 
@@ -228,8 +279,9 @@ TEST(ScrollViewTest, ScrollBars) {
   scroll_view.Layout();
   EXPECT_EQ(
       100 - scroll_view.GetScrollBarWidth() - kLeftPadding - kRightPadding,
-      contents->parent()->width());
-  EXPECT_EQ(100 - kTopPadding - kBottomPadding, contents->parent()->height());
+      test_api.contents_viewport()->width());
+  EXPECT_EQ(100 - kTopPadding - kBottomPadding,
+            test_api.contents_viewport()->height());
   EXPECT_TRUE(!scroll_view.horizontal_scroll_bar() ||
               !scroll_view.horizontal_scroll_bar()->visible());
   ASSERT_TRUE(scroll_view.vertical_scroll_bar() != NULL);
@@ -243,10 +295,11 @@ TEST(ScrollViewTest, ScrollBars) {
   // Horizontal with border.
   contents->SetBounds(0, 0, 400, 50);
   scroll_view.Layout();
-  EXPECT_EQ(100 - kLeftPadding - kRightPadding, contents->parent()->width());
+  EXPECT_EQ(100 - kLeftPadding - kRightPadding,
+            test_api.contents_viewport()->width());
   EXPECT_EQ(
       100 - scroll_view.GetScrollBarHeight() - kTopPadding - kBottomPadding,
-      contents->parent()->height());
+      test_api.contents_viewport()->height());
   ASSERT_TRUE(scroll_view.horizontal_scroll_bar() != NULL);
   EXPECT_TRUE(scroll_view.horizontal_scroll_bar()->visible());
   EXPECT_TRUE(!scroll_view.vertical_scroll_bar() ||
@@ -263,10 +316,10 @@ TEST(ScrollViewTest, ScrollBars) {
   scroll_view.Layout();
   EXPECT_EQ(
       100 - scroll_view.GetScrollBarWidth() - kLeftPadding - kRightPadding,
-      contents->parent()->width());
+      test_api.contents_viewport()->width());
   EXPECT_EQ(
       100 - scroll_view.GetScrollBarHeight() - kTopPadding - kBottomPadding,
-      contents->parent()->height());
+      test_api.contents_viewport()->height());
   bounds = scroll_view.horizontal_scroll_bar()->bounds();
   // Check horiz.
   ASSERT_TRUE(scroll_view.horizontal_scroll_bar() != NULL);
@@ -292,6 +345,7 @@ TEST(ScrollViewTest, ScrollBars) {
 // Assertions around adding a header.
 TEST(ScrollViewTest, Header) {
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   View* contents = new View;
   CustomView* header = new CustomView;
   scroll_view.SetHeader(header);
@@ -302,24 +356,25 @@ TEST(ScrollViewTest, Header) {
   // |header|s preferred size is empty, which should result in all space going
   // to contents.
   EXPECT_EQ("0,0 100x0", header->parent()->bounds().ToString());
-  EXPECT_EQ("0,0 100x100", contents->parent()->bounds().ToString());
+  EXPECT_EQ("0,0 100x100", test_api.contents_viewport()->bounds().ToString());
 
   // Get the header a height of 20.
   header->SetPreferredSize(gfx::Size(10, 20));
   EXPECT_EQ("0,0 100x20", header->parent()->bounds().ToString());
-  EXPECT_EQ("0,20 100x80", contents->parent()->bounds().ToString());
+  EXPECT_EQ("0,20 100x80", test_api.contents_viewport()->bounds().ToString());
 
   // Remove the header.
   scroll_view.SetHeader(NULL);
   // SetHeader(NULL) deletes header.
   header = NULL;
   EXPECT_EQ("0,0 100x0", header_parent->bounds().ToString());
-  EXPECT_EQ("0,0 100x100", contents->parent()->bounds().ToString());
+  EXPECT_EQ("0,0 100x100", test_api.contents_viewport()->bounds().ToString());
 }
 
 // Verifies the scrollbars are added as necessary when a header is present.
 TEST(ScrollViewTest, ScrollBarsWithHeader) {
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   View* contents = new View;
   scroll_view.SetContents(contents);
   CustomView* header = new CustomView;
@@ -331,10 +386,11 @@ TEST(ScrollViewTest, ScrollBarsWithHeader) {
   // Size the contents such that vertical scrollbar is needed.
   contents->SetBounds(0, 0, 50, 400);
   scroll_view.Layout();
-  EXPECT_EQ(0, contents->parent()->x());
-  EXPECT_EQ(20, contents->parent()->y());
-  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), contents->parent()->width());
-  EXPECT_EQ(80, contents->parent()->height());
+  EXPECT_EQ(0, test_api.contents_viewport()->x());
+  EXPECT_EQ(20, test_api.contents_viewport()->y());
+  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(),
+            test_api.contents_viewport()->width());
+  EXPECT_EQ(80, test_api.contents_viewport()->height());
   EXPECT_EQ(0, header->parent()->x());
   EXPECT_EQ(0, header->parent()->y());
   EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), header->parent()->width());
@@ -350,11 +406,11 @@ TEST(ScrollViewTest, ScrollBarsWithHeader) {
   // Size the contents such that horizontal scrollbar is needed.
   contents->SetBounds(0, 0, 400, 50);
   scroll_view.Layout();
-  EXPECT_EQ(0, contents->parent()->x());
-  EXPECT_EQ(20, contents->parent()->y());
-  EXPECT_EQ(100, contents->parent()->width());
+  EXPECT_EQ(0, test_api.contents_viewport()->x());
+  EXPECT_EQ(20, test_api.contents_viewport()->y());
+  EXPECT_EQ(100, test_api.contents_viewport()->width());
   EXPECT_EQ(100 - scroll_view.GetScrollBarHeight() - 20,
-            contents->parent()->height());
+            test_api.contents_viewport()->height());
   EXPECT_EQ(0, header->parent()->x());
   EXPECT_EQ(0, header->parent()->y());
   EXPECT_EQ(100, header->parent()->width());
@@ -367,11 +423,12 @@ TEST(ScrollViewTest, ScrollBarsWithHeader) {
   // Both horizontal and vertical.
   contents->SetBounds(0, 0, 300, 400);
   scroll_view.Layout();
-  EXPECT_EQ(0, contents->parent()->x());
-  EXPECT_EQ(20, contents->parent()->y());
-  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), contents->parent()->width());
+  EXPECT_EQ(0, test_api.contents_viewport()->x());
+  EXPECT_EQ(20, test_api.contents_viewport()->y());
+  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(),
+            test_api.contents_viewport()->width());
   EXPECT_EQ(100 - scroll_view.GetScrollBarHeight() - 20,
-            contents->parent()->height());
+            test_api.contents_viewport()->height());
   EXPECT_EQ(0, header->parent()->x());
   EXPECT_EQ(0, header->parent()->y());
   EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), header->parent()->width());
@@ -385,6 +442,7 @@ TEST(ScrollViewTest, ScrollBarsWithHeader) {
 // Verifies the header scrolls horizontally with the content.
 TEST(ScrollViewTest, HeaderScrollsWithContent) {
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   CustomView* contents = new CustomView;
   scroll_view.SetContents(contents);
   contents->SetPreferredSize(gfx::Size(500, 500));
@@ -394,44 +452,53 @@ TEST(ScrollViewTest, HeaderScrollsWithContent) {
   header->SetPreferredSize(gfx::Size(500, 20));
 
   scroll_view.SetBoundsRect(gfx::Rect(0, 0, 100, 100));
-  EXPECT_EQ("0,0", contents->bounds().origin().ToString());
+  EXPECT_EQ("0,0", test_api.IntegralViewOffset().ToString());
   EXPECT_EQ("0,0", header->bounds().origin().ToString());
 
   // Scroll the horizontal scrollbar.
   ASSERT_TRUE(scroll_view.horizontal_scroll_bar());
   scroll_view.ScrollToPosition(
       const_cast<ScrollBar*>(scroll_view.horizontal_scroll_bar()), 1);
-  EXPECT_EQ("-1,0", contents->bounds().origin().ToString());
+  EXPECT_EQ("-1,0", test_api.IntegralViewOffset().ToString());
   EXPECT_EQ("-1,0", header->bounds().origin().ToString());
 
   // Scrolling the vertical scrollbar shouldn't effect the header.
   ASSERT_TRUE(scroll_view.vertical_scroll_bar());
   scroll_view.ScrollToPosition(
       const_cast<ScrollBar*>(scroll_view.vertical_scroll_bar()), 1);
-  EXPECT_EQ("-1,-1", contents->bounds().origin().ToString());
+  EXPECT_EQ("-1,-1", test_api.IntegralViewOffset().ToString());
   EXPECT_EQ("-1,0", header->bounds().origin().ToString());
 }
 
 // Verifies ScrollRectToVisible() on the child works.
 TEST(ScrollViewTest, ScrollRectToVisible) {
+#if defined(OS_MACOSX)
+  ui::test::ScopedPreferredScrollerStyle scroller_style_override(false);
+#endif
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   CustomView* contents = new CustomView;
   scroll_view.SetContents(contents);
   contents->SetPreferredSize(gfx::Size(500, 1000));
 
   scroll_view.SetBoundsRect(gfx::Rect(0, 0, 100, 100));
   scroll_view.Layout();
-  EXPECT_EQ("0,0", contents->bounds().origin().ToString());
+  EXPECT_EQ("0,0", test_api.IntegralViewOffset().ToString());
 
   // Scroll to y=405 height=10, this should make the y position of the content
   // at (405 + 10) - viewport_height (scroll region bottom aligned).
   contents->ScrollRectToVisible(gfx::Rect(0, 405, 10, 10));
-  const int viewport_height = contents->parent()->height();
-  EXPECT_EQ(-(415 - viewport_height), contents->y());
+  const int viewport_height = test_api.contents_viewport()->height();
+
+  // Expect there to be a horizontal scrollbar, making the viewport shorter.
+  EXPECT_LT(viewport_height, 100);
+
+  gfx::ScrollOffset offset = test_api.CurrentOffset();
+  EXPECT_EQ(415 - viewport_height, offset.y());
 
   // Scroll to the current y-location and 10x10; should do nothing.
-  contents->ScrollRectToVisible(gfx::Rect(0, -contents->y(), 10, 10));
-  EXPECT_EQ(-(415 - viewport_height), contents->y());
+  contents->ScrollRectToVisible(gfx::Rect(0, offset.y(), 10, 10));
+  EXPECT_EQ(415 - viewport_height, test_api.CurrentOffset().y());
 }
 
 // Verifies ClipHeightTo() uses the height of the content when it is between the
@@ -577,6 +644,7 @@ TEST(ScrollViewTest, CocoaOverlayScrollBars) {
   scroller_style_override.reset(
       new ui::test::ScopedPreferredScrollerStyle(true));
   ScrollView scroll_view;
+  ScrollViewTestApi test_api(&scroll_view);
   View* contents = new View;
   scroll_view.SetContents(contents);
   scroll_view.SetBoundsRect(gfx::Rect(0, 0, 100, 100));
@@ -585,8 +653,8 @@ TEST(ScrollViewTest, CocoaOverlayScrollBars) {
   // Since it is overlaid, the ViewPort size should match the ScrollView.
   contents->SetBounds(0, 0, 50, 400);
   scroll_view.Layout();
-  EXPECT_EQ(100, contents->parent()->width());
-  EXPECT_EQ(100, contents->parent()->height());
+  EXPECT_EQ(100, test_api.contents_viewport()->width());
+  EXPECT_EQ(100, test_api.contents_viewport()->height());
   EXPECT_EQ(0, scroll_view.GetScrollBarWidth());
   CheckScrollbarVisibility(scroll_view, VERTICAL, true);
   CheckScrollbarVisibility(scroll_view, HORIZONTAL, false);
@@ -594,8 +662,8 @@ TEST(ScrollViewTest, CocoaOverlayScrollBars) {
   // Size the contents such that horizontal scrollbar is needed.
   contents->SetBounds(0, 0, 400, 50);
   scroll_view.Layout();
-  EXPECT_EQ(100, contents->parent()->width());
-  EXPECT_EQ(100, contents->parent()->height());
+  EXPECT_EQ(100, test_api.contents_viewport()->width());
+  EXPECT_EQ(100, test_api.contents_viewport()->height());
   EXPECT_EQ(0, scroll_view.GetScrollBarHeight());
   CheckScrollbarVisibility(scroll_view, VERTICAL, false);
   CheckScrollbarVisibility(scroll_view, HORIZONTAL, true);
@@ -603,8 +671,8 @@ TEST(ScrollViewTest, CocoaOverlayScrollBars) {
   // Both horizontal and vertical scrollbars.
   contents->SetBounds(0, 0, 300, 400);
   scroll_view.Layout();
-  EXPECT_EQ(100, contents->parent()->width());
-  EXPECT_EQ(100, contents->parent()->height());
+  EXPECT_EQ(100, test_api.contents_viewport()->width());
+  EXPECT_EQ(100, test_api.contents_viewport()->height());
   EXPECT_EQ(0, scroll_view.GetScrollBarWidth());
   EXPECT_EQ(0, scroll_view.GetScrollBarHeight());
   CheckScrollbarVisibility(scroll_view, VERTICAL, true);
@@ -620,9 +688,10 @@ TEST(ScrollViewTest, CocoaOverlayScrollBars) {
   // to be smaller, and ScrollbarWidth and ScrollbarHeight are non-zero.
   scroller_style_override.reset(
       new ui::test::ScopedPreferredScrollerStyle(false));
-  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(), contents->parent()->width());
+  EXPECT_EQ(100 - scroll_view.GetScrollBarWidth(),
+            test_api.contents_viewport()->width());
   EXPECT_EQ(100 - scroll_view.GetScrollBarHeight(),
-            contents->parent()->height());
+            test_api.contents_viewport()->height());
   EXPECT_NE(0, scroll_view.GetScrollBarWidth());
   EXPECT_NE(0, scroll_view.GetScrollBarHeight());
 }
@@ -661,4 +730,63 @@ TEST_F(WidgetScrollViewTest, ScrollTrackScrolling) {
   EXPECT_EQ(kDefaultHeight, scroll_view->GetVisibleRect().y());
 }
 
+// Test that views scroll offsets are in sync with the layer scroll offsets.
+TEST_F(WidgetScrollViewTest, ScrollOffsetUsingLayers) {
+  // Set up with a vertical scroller, but don't commit the layer changes yet.
+  ScrollView* scroll_view =
+      AddScrollViewWithContentSize(gfx::Size(10, kDefaultHeight * 5), false);
+  ScrollViewTestApi test_api(scroll_view);
+
+  EXPECT_EQ(gfx::ScrollOffset(0, 0), test_api.CurrentOffset());
+
+  // UI code may request a scroll before layer changes are committed.
+  gfx::Rect offset(0, kDefaultHeight * 2, 1, kDefaultHeight);
+  scroll_view->contents()->ScrollRectToVisible(offset);
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), test_api.CurrentOffset());
+
+  // The following only makes sense when layered scrolling is enabled.
+  View* container = test_api.contents_container();
+#if defined(OS_MACOSX)
+  // Sanity check: Mac should always scroll with layers.
+  EXPECT_TRUE(container);
+#endif
+  if (!container)
+    return;
+
+  // Container and viewport should have layers.
+  EXPECT_TRUE(container->layer());
+  EXPECT_TRUE(test_api.contents_viewport()->layer());
+
+  // In a Widget, so there should be a compositor.
+  ui::Compositor* compositor = container->layer()->GetCompositor();
+  EXPECT_TRUE(compositor);
+
+  // But setting on the impl side should fail since the layer isn't committed.
+  int layer_id = container->layer()->cc_layer_for_testing()->id();
+  EXPECT_FALSE(compositor->ScrollLayerTo(layer_id, gfx::ScrollOffset(0, 0)));
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), test_api.CurrentOffset());
+
+  WaitForCommit();
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), test_api.CurrentOffset());
+
+  // Upon commit, the impl side should report the same value too.
+  gfx::ScrollOffset impl_offset;
+  EXPECT_TRUE(compositor->GetScrollOffsetForLayer(layer_id, &impl_offset));
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), impl_offset);
+
+  // Now impl-side scrolling should work, and also update the ScrollView.
+  offset.set_y(kDefaultHeight * 3);
+  EXPECT_TRUE(
+      compositor->ScrollLayerTo(layer_id, gfx::ScrollOffset(0, offset.y())));
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), test_api.CurrentOffset());
+
+  // Scroll via ScrollView API. Should be reflected on the impl side.
+  offset.set_y(kDefaultHeight * 4);
+  scroll_view->contents()->ScrollRectToVisible(offset);
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), test_api.CurrentOffset());
+
+  EXPECT_TRUE(compositor->GetScrollOffsetForLayer(layer_id, &impl_offset));
+  EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), impl_offset);
+}
+
 }  // namespace views