Handle position:absolute candidates correctly in ScrollAnchor.

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"
 
@@ skipping 162 matching lines @@
         "<div id=f>fixed</div>"
         "<div id=c>content</div>");
 
     scrollLayoutViewport(DoubleSize(0, 50));
 
     setHeight(document().body(), 1100);
     EXPECT_EQ(document().getElementById("c")->layoutObject(),
         scrollAnchor(layoutViewport()).anchorObject());
 }
 
+TEST_F(ScrollAnchorTest, ExcludeAbsolutePosition)
+{
+    setBodyInnerHTML(
+        "<style>"
+        "    body { margin: 0; }"
+        "    #scroller { overflow: scroll; width: 500px; height: 400px; }"
+        "    #space { height: 1000px; }"
+        "    #abs {"
+        "        position: absolute; background-color: red;"
+        "        left: 200px; top: 100px; width: 100px; height: 100px;"
+        "    }"
+        "    #rel {"
+        "        position: relative; background-color: green;"
+        "        left: 50px; top: 100px; width: 100px; height: 75px;"
+        "    }"
+        "</style>"
+        "<div id='scroller'><div id='space'>"
+        "    <div id='abs'></div>"
+        "    <div id='rel'></div>"
+        "</div></div>");
+
+    Element* scrollerElement = document().getElementById("scroller");
+    ScrollableArea* scroller = scrollerForElement(scrollerElement);
+    Element* absPos = document().getElementById("abs");
+    Element* relPos = document().getElementById("rel");
+
+    scroller->scrollBy(DoubleSize(0, 25), UserScroll);
+    setHeight(relPos, 100);
+
+    // When the scroller is position:static, the anchor cannot be position:absolute.
+    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());
+}
+
 class ScrollAnchorCornerTest : public ScrollAnchorTest {
 protected:
     void checkCorner(const AtomicString& id, Corner corner, DoublePoint startPos, DoubleSize expectedAdjustment)
     {
         ScrollableArea* viewport = layoutViewport();
         Element* element = document().getElementById(id);
 
         viewport->setScrollPosition(startPos, UserScroll);
         element->setAttribute(HTMLNames::classAttr, "big");
         update();
@@ skipping 33 matching lines @@
         "<div id=c></div>"
         "<div id=d></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));
 }
 
 }