Mark elements as viewport constrained when they become sticky positioned

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/LayoutBoxModelObject.h"
 
 #include "core/dom/DOMTokenList.h"
 #include "core/dom/DocumentLifecycle.h"
 #include "core/html/HTMLElement.h"
 #include "core/layout/ImageQualityController.h"
@@ skipping 310 matching lines @@
 
   // After updating compositing inputs we should have the updated position.
   document().view()->updateAllLifecyclePhases();
   EXPECT_EQ(50.f,
             getScrollContainerRelativeStickyBoxRect(
                 scrollableArea->stickyConstraintsMap().get(sticky->layer()))
                 .location()
                 .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