Handle nested position:sticky elements correctly (compositor)

cc/layers/layer_sticky_position_constraint.cc

Index: cc/layers/layer_sticky_position_constraint.cc
diff --git a/cc/layers/layer_sticky_position_constraint.cc b/cc/layers/layer_sticky_position_constraint.cc
index 79414d6a8775daeb4d3a0a67a9b4717cdb61432e..bb7478734cee8db4abbb1ab0540e27be515fbd0b 100644
--- a/cc/layers/layer_sticky_position_constraint.cc
+++ b/cc/layers/layer_sticky_position_constraint.cc
@@ -15,7 +15,9 @@ LayerStickyPositionConstraint::LayerStickyPositionConstraint()
       left_offset(0.f),
       right_offset(0.f),
       top_offset(0.f),
-      bottom_offset(0.f) {}
+      bottom_offset(0.f),
+      nearest_layer_shifting_sticky_box(nullptr),
+      nearest_layer_shifting_containing_block(nullptr) {}
 
 LayerStickyPositionConstraint::LayerStickyPositionConstraint(
     const LayerStickyPositionConstraint& other)
@@ -33,7 +35,15 @@ LayerStickyPositionConstraint::LayerStickyPositionConstraint(
       scroll_container_relative_sticky_box_rect(
           other.scroll_container_relative_sticky_box_rect),
       scroll_container_relative_containing_block_rect(
-          other.scroll_container_relative_containing_block_rect) {}
+          other.scroll_container_relative_containing_block_rect),
+      nearest_layer_shifting_sticky_box(
+          other.nearest_layer_shifting_sticky_box),
+      nearest_layer_shifting_containing_block(
+          other.nearest_layer_shifting_containing_block),
+      total_sticky_box_sticky_offset(other.total_sticky_box_sticky_offset),
+      total_containing_block_sticky_offset(
+          other.total_containing_block_sticky_offset),
+      local_sticky_offset(other.local_sticky_offset) {}
 
 bool LayerStickyPositionConstraint::operator==(
     const LayerStickyPositionConstraint& other) const {
@@ -52,7 +62,16 @@ bool LayerStickyPositionConstraint::operator==(
          scroll_container_relative_sticky_box_rect ==
              other.scroll_container_relative_sticky_box_rect &&
          scroll_container_relative_containing_block_rect ==
-             other.scroll_container_relative_containing_block_rect;
+             other.scroll_container_relative_containing_block_rect &&
+         nearest_layer_shifting_sticky_box ==
+             other.nearest_layer_shifting_sticky_box &&
+         nearest_layer_shifting_containing_block ==
+             other.nearest_layer_shifting_containing_block &&
+         total_sticky_box_sticky_offset ==
+             other.total_sticky_box_sticky_offset &&
+         total_containing_block_sticky_offset ==
+             other.total_containing_block_sticky_offset &&
+         local_sticky_offset == other.local_sticky_offset;
 }
 
 bool LayerStickyPositionConstraint::operator!=(