Implement PaintArtifactCompositor::mightOverlap.

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

Index: third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
index 00b42f49923192a032fd0eac271336db5f9aa865..0ed85739180563bfd65c28b2008e2d726ca40336 100644
--- a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
+++ b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp
@@ -1041,8 +1041,25 @@ bool PaintArtifactCompositor::mightOverlap(
     const PaintChunk& paintChunk,
     const PendingLayer& candidatePendingLayer,
     GeometryMapper& geometryMapper) {
-  // TODO(chrishtr): implement
-  return true;
+  PropertyTreeState rootPropertyTreeState(

[wkorman, 2016/12/29 19:49:40]

nit: could be worth adding a static instance for this, following what we do for
the root nodes themselves. We use this in a few other places already though
they're all tests until this case. Could replace those with this if we had it,
but mainly, might make overlap tests a bit faster since we wouldn't need to
construct each time. Premature optimization, etc.

[chrishtr, 2016/12/29 19:52:29]

Good idea. I have a cleanup CL for PaintArtifactCompositorTest queued up that is
sort of related to this, will this change to it.

+      TransformPaintPropertyNode::root(), ClipPaintPropertyNode::root(),
+      EffectPaintPropertyNode::root(), ScrollPaintPropertyNode::root());
+
+  bool success = false;
+  FloatRect paintChunkScreenVisualRect =
+      geometryMapper.localToVisualRectInAncestorSpace(
+          paintChunk.bounds, paintChunk.properties.propertyTreeState,
+          rootPropertyTreeState, success);
+  DCHECK(success);
+
+  success = false;
+  FloatRect pendingLayerScreenVisualRect =
+      geometryMapper.localToVisualRectInAncestorSpace(
+          candidatePendingLayer.bounds, candidatePendingLayer.propertyTreeState,
+          rootPropertyTreeState, success);
+  DCHECK(success);
+
+  return paintChunkScreenVisualRect.intersects(pendingLayerScreenVisualRect);
 }
 
 PaintArtifactCompositor::PendingLayer::PendingLayer(