Force subtree paint property updates on local border box changes

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilderTest.cpp

 // Copyright 2015 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/html/HTMLIFrameElement.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/LayoutTreeAsText.h"
 #include "core/layout/api/LayoutViewItem.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintPropertyTreePrinter.h"
@@ skipping 3213 matching lines @@
 TEST_P(PaintPropertyTreeBuilderTest, NoPaintPropertyUpdateOnBackgroundChange) {
   setBodyInnerHTML("<div id='div' style='background-color: blue'>DIV</div>");
   auto* div = document().getElementById("div");
 
   document().view()->updateAllLifecyclePhases();
   div->setAttribute(HTMLNames::styleAttr, "background-color: green");
   document().view()->updateLifecycleToLayoutClean();
   EXPECT_FALSE(div->layoutObject()->needsPaintPropertyUpdate());
 }
 
+TEST_P(PaintPropertyTreeBuilderTest, LocalBorderBoxChanges) {

[chrishtr, 2016/12/15 19:42:52]

For completeness, please also add a test for position: fixed.

+  setBodyInnerHTML(
+      "<style>"
+      "  body { margin: 0 }"
+      "  #scroller { width: 3px; height: 5px; overflow: scroll; }"
+      "  #child { top: 0; left: 0; }"
+      "</style>"
+      "<div id='scroller'>"
+      "  <div id='child'>"
+      "    <div id='grandChild'></div>"
+      "  </div>"
+      "</div>");
+  document().view()->updateAllLifecyclePhases();
+  auto* grandChild = document().getElementById("grandChild");
+  auto* grandChildProperties = grandChild->layoutObject()->paintProperties();
+  auto* localBorderBox = grandChildProperties->localBorderBoxProperties();
+  EXPECT_EQ(FloatRect(0, 0, 3, 5),
+            localBorderBox->propertyTreeState.clip()->clipRect().rect());
+
+  // Update the scroller's transform value but ensure the child's paint offset
+  // is unchanged so subtree updates are not forced by paint offset changes.
+  auto* scroller = document().getElementById("scroller");
+  scroller->setScrollTop(7);
+  auto* child = document().getElementById("child");
+  child->setAttribute(HTMLNames::styleAttr, "position: absolute");
+  document().view()->updateAllLifecyclePhases();
+  EXPECT_EQ(FloatRect(0, 0, 800, 600),

[chrishtr, 2016/12/15 19:42:52]

Also check its transform node and scroll node to see that it's the root and not
the scroller.

And an example with effects?

+            localBorderBox->propertyTreeState.clip()->clipRect().rect());
+}
+
 }  // namespace blink