[DNS] Don't adjust the scroll position if the anchor element changes in size

third_party/WebKit/Source/core/layout/ScrollAnchorTest.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/layout/ScrollAnchor.h"
 
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "platform/testing/HistogramTester.h"
@@ skipping 228 matching lines @@
     EXPECT_EQ(relPos->layoutObject(), scrollAnchor(scroller).anchorObject());
 
     scrollerElement->setAttribute(HTMLNames::styleAttr, "position: relative");
     scroller->scrollBy(DoubleSize(0, 25), UserScroll);
     setHeight(relPos, 125);
 
     // When the scroller is position:relative, the anchor may be position:absolute.
     EXPECT_EQ(absPos->layoutObject(), scrollAnchor(scroller).anchorObject());
 }
 
+// See crbug.com/600891 for context as to why we don't adjust the scroll offset
+// if the anchor node changes.
+TEST_F(ScrollAnchorTest, NoAdjustmentIfAnchorChanged)
+{
+    setBodyInnerHTML(
+        "<style>"
+        "   body { height: 2000px; }"
+        "   #beforeAnchor {"
+        "       height: 300px; background-color: #fcc;"
+        "   }"
+        "   #anchor {"
+        "       background-color: #afa;  height: 200px; border: 1px solid gray;"
+        "   }"
+        "</style>"
+        "<div id=beforeAnchor></div>"
+        "<div id=anchor></div>");
+
+    // Bring div that will be anchored into view and change it's height.
+    scrollLayoutViewport(DoubleSize(0, 350));
+    setHeight(document().getElementById("anchor"), 300);
+    // No adjustment should be made.
+    EXPECT_EQ(DoublePoint(0, 350), layoutViewport()->scrollPositionDouble());
+}
+
 class ScrollAnchorCornerTest : public ScrollAnchorTest {
 protected:
-    void checkCorner(const AtomicString& id, Corner corner, DoublePoint startPos, DoubleSize expectedAdjustment)
+    void checkCorner(const AtomicString& expectedAnchorId, Corner corner, DoublePoint startPos, DoubleSize expectedAdjustment)
     {
         ScrollableArea* viewport = layoutViewport();
-        Element* element = document().getElementById(id);
+        Element* changingElement = document().getElementById("changer");
+        viewport->setScrollPosition(startPos, UserScroll);
 
-        viewport->setScrollPosition(startPos, UserScroll);
-        element->setAttribute(HTMLNames::classAttr, "big");
-        update();
+        setHeight(changingElement, 200);
 
         DoublePoint endPos = startPos;
         endPos.move(expectedAdjustment);
 
         EXPECT_EQ(endPos, viewport->scrollPositionDouble());
-        EXPECT_EQ(element->layoutObject(), scrollAnchor(viewport).anchorObject());
+        EXPECT_EQ(document().getElementById(expectedAnchorId)->layoutObject(),
+            scrollAnchor(viewport).anchorObject());
         EXPECT_EQ(corner, scrollAnchor(viewport).corner());
 
-        element->removeAttribute(HTMLNames::classAttr);
-        update();
+        setHeight(changingElement, 0);
     }
 };
 
 TEST_F(ScrollAnchorCornerTest, Corners)
 {
     setBodyInnerHTML(
         "<style>"
-        "    body {"
-        "        position: absolute; border: 10px solid #ccc;"
+        "    #container {"
+        "        position: relative; border: 1px solid black;"
         "        width: 1220px; height: 920px;"
         "    }"
         "    #a, #b, #c, #d {"
         "        position: absolute; background-color: #ace;"
         "        width: 400px; height: 300px;"
         "    }"
         "    #a, #b { top: 0; }"
         "    #a, #c { left: 0; }"
         "    #b, #d { right: 0; }"
         "    #c, #d { bottom: 0; }"
-        "    .big { width: 800px !important; height: 600px !important }"
         "</style>"
-        "<div id=a></div>"
-        "<div id=b></div>"
-        "<div id=c></div>"
-        "<div id=d></div>");
+        "<div id=changer></div>"
+        "<div id=container>"
+        "   <div id=a></div>"
+        "   <div id=b></div>"
+        "   <div id=c></div>"
+        "   <div id=d></div>"
+        "</div>");
 
-    checkCorner("a", Corner::BottomRight, DoublePoint(20,  20),  DoubleSize(+400, +300));
-    checkCorner("b", Corner::BottomLeft,  DoublePoint(420, 20),  DoubleSize(-400, +300));
-    checkCorner("c", Corner::TopRight,    DoublePoint(20,  320), DoubleSize(+400, -300));
-    checkCorner("d", Corner::TopLeft,     DoublePoint(420, 320), DoubleSize(-400, -300));
+    checkCorner("a", Corner::BottomRight, DoublePoint(20,  20),  DoubleSize(0, 200));
+    checkCorner("b", Corner::BottomLeft,  DoublePoint(420, 20),  DoubleSize(0, 200));
+    checkCorner("c", Corner::TopRight,    DoublePoint(20,  320), DoubleSize(0, 200));
+    checkCorner("d", Corner::TopLeft,     DoublePoint(420, 320), DoubleSize(0, 200));
 }
 
 }