Mark elements as viewport constrained when they become sticky positioned

third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
index ca16f0c6be9a2f1ec16ff0bf5dd4f3dcc545b033..133df0a09698577c163f223d3240aa827aa6db65 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
@@ -328,4 +328,32 @@ TEST_F(LayoutBoxModelObjectTest, StickyPositionConstraintInvalidation) {
                 .x());
 }
 
+TEST_F(LayoutBoxModelObjectTest, StyleChangesUpdateViewportConstrainedObjects) {
+  setBodyInnerHTML(
+      "<style>"
+      ".container { height: 200%; }"
+      "#sticky { position: sticky; top: 0; height: 50px; }</style>"
+      "<div class='container'><div id='sticky'></div></div>");
+
+  LayoutBoxModelObject* sticky =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("sticky"));
+
+  EXPECT_TRUE(
+      document().view()->viewportConstrainedObjects()->contains(sticky));
+
+  RefPtr<ComputedStyle> relativeStyle = ComputedStyle::clone(*sticky->style());
+  relativeStyle->setPosition(EPosition::kRelative);
+  sticky->setStyle(relativeStyle.get());
+
+  EXPECT_FALSE(
+      document().view()->viewportConstrainedObjects()->contains(sticky));
+
+  RefPtr<ComputedStyle> stickyStyle = ComputedStyle::clone(*sticky->style());
+  stickyStyle->setPosition(EPosition::kSticky);
+  sticky->setStyle(stickyStyle.get());
+
+  EXPECT_TRUE(
+      document().view()->viewportConstrainedObjects()->contains(sticky));
+}
+
 }  // namespace blink