Note scrollbar layer properties changed when position changes.

cc/trees/layer_tree_host_unittest_damage.cc

Index: cc/trees/layer_tree_host_unittest_damage.cc
diff --git a/cc/trees/layer_tree_host_unittest_damage.cc b/cc/trees/layer_tree_host_unittest_damage.cc
index e8ae7a211f2f3d0fef7149d1b8a1345cae81e270..c130404589cbd15111bdde47628280da7f9d0191 100644
--- a/cc/trees/layer_tree_host_unittest_damage.cc
+++ b/cc/trees/layer_tree_host_unittest_damage.cc
@@ -6,6 +6,7 @@
 
 #include "cc/test/fake_content_layer.h"
 #include "cc/test/fake_content_layer_client.h"
+#include "cc/test/fake_scrollbar_layer.h"
 #include "cc/test/layer_tree_test.h"
 #include "cc/trees/damage_tracker.h"
 #include "cc/trees/layer_tree_impl.h"
@@ -285,5 +286,87 @@ class LayerTreeHostDamageTestForcedFullDamage : public LayerTreeHostDamageTest {
 
 SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostDamageTestForcedFullDamage);
 
+class LayerTreeHostDamageTestScrollbarDoesDamage
+    : public LayerTreeHostDamageTest {
+  virtual void BeginTest() OVERRIDE {
+    did_swaps_ = 0;
+    PostSetNeedsCommitToMainThread();
+  }
+
+  virtual void SetupTree() OVERRIDE {
+    layer_tree_root_ = Layer::Create();

[danakj, 2013/08/14 21:29:14]

does this need to be a member variable? usually they all do or none of them do.
i don't see you using this on the main thread outside of this function. (nit:
root_layer? layer_tree_root reads a lot like layer_tree_host :))

+    scoped_refptr<Layer> content_layer = FakeContentLayer::Create(&client_);
+    scoped_refptr<Layer> scrollbar_layer =
+        FakeScrollbarLayer::Create(false, true, content_layer->id());
+    layer_tree_root_->AddChild(content_layer);

[danakj, 2013/08/14 21:29:14]

nit: some whitespace in between blocks of calls for each layer object would
help, and grouping the creation at the top of each block for the calls on that
layer.

+    layer_tree_root_->AddChild(scrollbar_layer);
+    layer_tree_host()->SetRootLayer(layer_tree_root_);
+    content_layer->SetScrollable(true);
+    content_layer->SetScrollOffset(gfx::Vector2d(10, 20));
+    content_layer->SetMaxScrollOffset(gfx::Vector2d(30, 50));
+    content_layer->SetBounds(gfx::Size(100, 200));
+    scrollbar_layer->SetPosition(gfx::Point(300, 300));
+    scrollbar_layer->SetBounds(gfx::Size(10, 100));
+    layer_tree_root_->SetBounds(gfx::Size(400,400));
+    LayerTreeHostDamageTest::SetupTree();

[danakj, 2013/08/14 21:29:14]

can you EXPECT here that the content_layer does not contain the scrollbar, so we
know the test is doing what it claims for all time?

+  }
+
+  virtual bool PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
+                                     LayerTreeHostImpl::FrameData* frame_data,
+                                     bool result) OVERRIDE {
+    EXPECT_TRUE(result);
+    RenderSurfaceImpl* root_surface =
+        host_impl->active_tree()->root_layer()->render_surface();
+    gfx::RectF root_damage =
+        root_surface->damage_tracker()->current_damage_rect();
+    root_damage.Intersect(root_surface->content_rect());
+    switch (did_swaps_) {
+      case 0:
+        // The first frame has damage, so we should draw and swap.
+        break;
+      case 1:
+        // The second frame should damage the scrollbars.
+        EXPECT_TRUE(root_damage.Contains(gfx::Rect(300, 300, 10, 100)));
+        break;
+      case 2:
+        // The third frame should not damage the scrollbars.
+        EXPECT_FALSE(root_damage.Contains(gfx::Rect(300, 300, 10, 100)));

[enne (OOO), 2013/08/14 21:33:41]

Can Contains be changed to Intersects here to be more stringent?

+        EndTest();
+        break;
+    }
+    return result;
+  }
+
+  virtual void SwapBuffersOnThread(LayerTreeHostImpl* host_impl,
+                                   bool result) OVERRIDE {
+    ++did_swaps_;
+    EXPECT_TRUE(result);
+    switch (did_swaps_) {
+      case 1:
+        host_impl->ScrollBegin(gfx::Point(1,1), InputHandler::Wheel);
+        EXPECT_TRUE(host_impl->ScrollBy(gfx::Point(),
+                                        gfx::Vector2dF(10.0, 10.0)));
+        break;
+      case 2:

[danakj, 2013/08/14 21:29:14]

Can you add a case that changes the max scroll (thumb size)?

+        host_impl->ScheduleAnimation();

[danakj, 2013/08/14 21:29:14]

nit: SetNeedsRedraw() instead?

+        LayerImpl* root = host_impl->active_tree()->root_layer();
+
+        root->children()[0]->SetPosition(gfx::Point(1,1));

[danakj, 2013/08/14 21:29:14]

Add a comment explaining what this case is doing and why it is testing the
scrollbar?

+        break;
+    }
+
+  }
+
+  virtual void AfterTest() OVERRIDE {
+    EXPECT_EQ(3, did_swaps_);
+  }
+
+  FakeContentLayerClient client_;
+  scoped_refptr<Layer> layer_tree_root_;
+  int did_swaps_;
+};
+
+MULTI_THREAD_TEST_F(LayerTreeHostDamageTestScrollbarDoesDamage);
+
 }  // namespace
 }  // namespace cc