Fixed rounding issue on scrollbar rasterization.

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 2d01af7289db11f50c91955a9dab07485f31f687..09570ac319dbc2c77cefcd138beb7c4d916e4e01 100644
--- a/cc/layers/scrollbar_layer_unittest.cc
+++ b/cc/layers/scrollbar_layer_unittest.cc
@@ -29,6 +29,9 @@
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+using ::testing::_;
+using ::testing::Invoke;
+
 namespace cc {
 namespace {
 
@@ -766,5 +769,74 @@ TEST_F(ScaledScrollbarLayerTestResourceCreation, ScaledResourceUpload) {
   TestResourceUpload(4.1f);
 }
 
+class ScaledScrollbarLayerTestScaledRasterization : public testing::Test {
+  class MockScrollbar : public FakeScrollbar {
+   public:
+    MockScrollbar(bool paint, bool has_thumb, bool is_overlay)
+    : FakeScrollbar(paint, has_thumb, is_overlay)
+    {}
+
+    MOCK_METHOD3(PaintPart, void(SkCanvas* canvas,
+                                 ScrollbarPart part,
+                                 const gfx::Rect& content_rect));
+  };
+
+ public:
+  ScaledScrollbarLayerTestScaledRasterization()
+      : fake_client_(FakeLayerTreeHostClient::DIRECT_3D) {}
+
+  void TestScale(const gfx::Rect scrollbar_rect, const float test_scale) {
+    layer_tree_host_.reset(
+        new MockLayerTreeHost(&fake_client_, layer_tree_settings_));
+
+    MockScrollbar* mock_scrollbar = new MockScrollbar(false, false, false);
+    scoped_refptr<Layer> layer_tree_root = Layer::Create();
+    scoped_refptr<FakePaintedScrollbarLayer> scrollbar_layer =
+        FakePaintedScrollbarLayer::Create(false, false, layer_tree_root->id(),
+                                          mock_scrollbar);
+
+    layer_tree_root->AddChild(scrollbar_layer);
+
+    layer_tree_host_->SetRootLayer(layer_tree_root);
+
+    scrollbar_layer->SetBounds(scrollbar_rect.size());
+    scrollbar_layer->SetPosition(scrollbar_rect.origin());
+    scrollbar_layer->fake_scrollbar()->set_location(scrollbar_rect.origin());
+    gfx::SizeF scaled_size =
+        gfx::ScaleSize(scrollbar_layer->bounds(), test_scale, test_scale);
+    gfx::PointF scaled_location =
+        gfx::ScalePoint(scrollbar_layer->position(), test_scale, test_scale);
+    scrollbar_layer->draw_properties().content_bounds =
+        gfx::Size(scaled_size.width(), scaled_size.height());
+    scrollbar_layer->draw_properties().contents_scale_x = test_scale;
+    scrollbar_layer->draw_properties().contents_scale_y = test_scale;
+    scrollbar_layer->draw_properties().visible_content_rect =
+        gfx::Rect(scaled_location.x(),
+                  scaled_location.y(),
+                  scaled_size.width(),
+                  scaled_size.height());
+
+    ResourceUpdateQueue queue;
+    OcclusionTracker occlusion_tracker(gfx::Rect(), false);
+    scrollbar_layer->SavePaintProperties();
+
+    EXPECT_CALL(*mock_scrollbar, PaintPart(_, TRACK, scrollbar_rect));
+
+    scrollbar_layer->Update(&queue, &occlusion_tracker);
+    scrollbar_layer->ClearRenderSurface();
+  }
+
+ protected:
+  FakeLayerTreeHostClient fake_client_;
+  LayerTreeSettings layer_tree_settings_;
+  scoped_ptr<MockLayerTreeHost> layer_tree_host_;
+};
+
+TEST_F(ScaledScrollbarLayerTestScaledRasterization, TestLostPrecisionInClip) {
+  // Try rasterization at a scale that caused problematic floating point
+  // clamping causing a black line on scrollbar edges.
+  TestScale(gfx::Rect(1117, 0, 15, 677), 7.301320);
+}
+
 }  // namespace
 }  // namespace cc