Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp

Index: third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp
index 889a1b6298b3d70396609c2e53162d003ff355ce..5dd795ed2319cda2be1b601ba235d95e66dfd712 100644
--- a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp
+++ b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.cpp
@@ -705,6 +705,47 @@ TEST_F(PaintArtifactCompositorTestWithPropertyTrees, OneScrollNode) {
             scrollNode.main_thread_scrolling_reasons);
 }
 
+TEST_F(PaintArtifactCompositorTestWithPropertyTrees, TransformUnderScrollNode) {
+  RefPtr<TransformPaintPropertyNode> scrollTranslation =
+      TransformPaintPropertyNode::createScrollTranslation(
+          TransformPaintPropertyNode::root(),
+          TransformationMatrix().translate(7, 9), FloatPoint3D(), false, 0,
+          CompositingReasonNone, CompositorElementId(),
+          ScrollPaintPropertyNode::root(), IntSize(11, 13), IntSize(27, 31),
+          true, false, 0 /* mainThreadScrollingReasons */);
+
+  RefPtr<TransformPaintPropertyNode> transform =
+      TransformPaintPropertyNode::create(
+          scrollTranslation, TransformationMatrix(), FloatPoint3D(), false, 0,
+          CompositingReason3DTransform);
+
+  TestPaintArtifact artifact;
+  artifact
+      .chunk(scrollTranslation, ClipPaintPropertyNode::root(),
+             EffectPaintPropertyNode::root())
+      .rectDrawing(FloatRect(2, 4, 6, 8), Color::black)
+      .chunk(transform, ClipPaintPropertyNode::root(),
+             EffectPaintPropertyNode::root())
+      .rectDrawing(FloatRect(1, 3, 5, 7), Color::white);
+  update(artifact.build());
+
+  const cc::ScrollTree& scrollTree = propertyTrees().scroll_tree;
+  // Node #0 reserved for null; #1 for root render surface.
+  ASSERT_EQ(3u, scrollTree.size());
+  const cc::ScrollNode& scrollNode = *scrollTree.Node(2);
+
+  // Both layers should refer to the same scroll tree node.
+  EXPECT_EQ(scrollNode.id, contentLayerAt(0)->scroll_tree_index());
+  EXPECT_EQ(scrollNode.id, contentLayerAt(1)->scroll_tree_index());
+
+  const cc::TransformTree& transformTree = propertyTrees().transform_tree;
+  const cc::TransformNode& scrollTransformNode =
+      *transformTree.Node(scrollNode.transform_id);
+  // The layers have different transform nodes.
+  EXPECT_EQ(scrollTransformNode.id, contentLayerAt(0)->transform_tree_index());

[pdr., 2017/02/02 04:22:32]

There is not yet any end-to-end infrastructure for impl-side hit testing so a
simple unit test has been added instead. I'm not a huge fan of this but
discussed it with Ajuma and we think it's a reasonable approach for now. For
ease of sleeping I am telling myself the test does add some coverage of
PaintArtifactCompositor setting scroll and transform values on cc:layer that
wasn't present before.

+  EXPECT_NE(scrollTransformNode.id, contentLayerAt(1)->transform_tree_index());
+}
+
 TEST_F(PaintArtifactCompositorTestWithPropertyTrees, NestedScrollNodes) {
   RefPtr<EffectPaintPropertyNode> effect =
       createOpacityOnlyEffect(EffectPaintPropertyNode::root(), 0.5);