Ignore rounding error between clip_layer_length_ and scroll_layer_length_

cc/layers/scrollbar_layer_unittest.cc

Index: cc/layers/scrollbar_layer_unittest.cc
diff --git a/cc/layers/scrollbar_layer_unittest.cc b/cc/layers/scrollbar_layer_unittest.cc
index 68613e87e33360ad4da748168d35c9d155151e2f..8cc778b9e9cbc03541a03c2a40c68ca891f9d19c 100644
--- a/cc/layers/scrollbar_layer_unittest.cc
+++ b/cc/layers/scrollbar_layer_unittest.cc
@@ -26,6 +26,7 @@
 #include "cc/test/fake_painted_scrollbar_layer.h"
 #include "cc/test/fake_scrollbar.h"
 #include "cc/test/geometry_test_utils.h"
+#include "cc/test/layer_test_common.h"
 #include "cc/test/layer_tree_test.h"
 #include "cc/test/mock_occlusion_tracker.h"
 #include "cc/test/stub_layer_tree_host_single_thread_client.h"
@@ -766,6 +767,48 @@ TEST_F(ScrollbarLayerTest, ScrollbarLayerPushProperties) {
   EXPECT_EQ(node->opacity, 1.f);
 }
 
+TEST_F(ScrollbarLayerTest, SubPixelCanScrollOrientation) {
+  gfx::Size viewport_size(100, 100);
+
+  LayerTestCommon::LayerImplTest impl;
+
+  LayerImpl* clip_layer = impl.AddChildToRoot<LayerImpl>();
+  LayerImpl* scroll_layer = impl.AddChild<LayerImpl>(clip_layer);
+
+  scroll_layer->SetScrollClipLayer(clip_layer->id());
+
+  const int kTrackStart = 0;
+  const int kThumbThickness = 10;
+  const bool kIsLeftSideVerticalScrollbar = false;
+  const bool kIsOverlayScrollbar = false;
+
+  SolidColorScrollbarLayerImpl* scrollbar_layer =
+      impl.AddChild<SolidColorScrollbarLayerImpl>(
+          scroll_layer, HORIZONTAL, kThumbThickness, kTrackStart,
+          kIsLeftSideVerticalScrollbar, kIsOverlayScrollbar);
+
+  scrollbar_layer->SetScrollInfo(scroll_layer->id(),
+                                 scrollbar_layer->element_id());
+  clip_layer->SetBounds(gfx::Size(100, 100));
+  scroll_layer->SetBounds(gfx::Size(100, 100));
+
+  impl.CalcDrawProps(viewport_size);
+
+  // Fake device scale.
+  impl.host_impl()->active_tree()->SetDeviceScaleFactor(3);
+
+  // Fake clip layer length to scrollbar to mock rounding error.
+  scrollbar_layer->SetClipLayerLength(99.99f);
+
+  EXPECT_FALSE(scrollbar_layer->CanScrollOrientation());
+
+  // Fake clip layer length to scrollbar to 1 device pixel shorter than scroll
+  // layer.
+  scrollbar_layer->SetClipLayerLength(99.65f);
+
+  EXPECT_TRUE(scrollbar_layer->CanScrollOrientation());
+}
+
 class ScrollbarLayerSolidColorThumbTest : public testing::Test {
  public:
   ScrollbarLayerSolidColorThumbTest() {