Align physical pixels of scrolled layers

cc/layer_tree_host_common_unittest.cc

Index: cc/layer_tree_host_common_unittest.cc
diff --git a/cc/layer_tree_host_common_unittest.cc b/cc/layer_tree_host_common_unittest.cc
index 655bbaf5dd79890bc67ed3762c78748111f9fd3c..00245a50bc740d32ce7f3a156b59493511caa456 100644
--- a/cc/layer_tree_host_common_unittest.cc
+++ b/cc/layer_tree_host_common_unittest.cc
@@ -258,6 +258,34 @@ TEST(LayerTreeHostCommonTest, verifyTransformsForSingleLayer)
     EXPECT_TRANSFORMATION_MATRIX_EQ(expectedResult, layer->screenSpaceTransform());
 }
 
+TEST(LayerTreeHostCommonTest, verifyTransformsAboutScrollOffset)
+{
+    const gfx::Vector2d kScrollOffset(50, 100);
+    const gfx::Vector2dF kScrollDelta(2.34, 5.67);
+    const gfx::PointF kLayerPosition(-(kScrollOffset.x() + kScrollDelta.x()), -(kScrollOffset.y() + kScrollDelta.y()));
+
+    FakeImplProxy proxy;
+    FakeLayerTreeHostImpl hostImpl(&proxy);
+
+    gfx::Transform identityMatrix;
+    scoped_ptr<LayerImpl> layerScopedPtr(LayerImpl::create(hostImpl.activeTree(), 1));
+    LayerImpl* layer = layerScopedPtr.get();
+    layer->setDrawsContent(true);
+    setLayerPropertiesForTesting(layer, identityMatrix, identityMatrix, gfx::Point(0, 0), kLayerPosition, gfx::Size(500, 500), false);
+
+    scoped_ptr<LayerImpl> root(LayerImpl::create(hostImpl.activeTree(), 2));
+    setLayerPropertiesForTesting(root.get(), identityMatrix, identityMatrix, gfx::PointF(0, 0), gfx::PointF(0, 0), gfx::Size(10, 20), false);
+    root->setScrollable(true);
+    root->setScrollOffset(kScrollOffset);
+    root->setScrollDelta(kScrollDelta);
+    root->addChild(layerScopedPtr.Pass());
+
+    executeCalculateDrawProperties(root.get(), 1, 1.5);
+    gfx::Transform expectedTransform = identityMatrix;
+    expectedTransform.Translate(round(kLayerPosition.x()), round(kLayerPosition.y()));
+    EXPECT_TRANSFORMATION_MATRIX_EQ(expectedTransform, layer->drawTransform());
+}
+
 TEST(LayerTreeHostCommonTest, verifyTransformsForSimpleHierarchy)
 {
     gfx::Transform identityMatrix;