Round anchor offsets to DIPs in ScrollAnchor::restore.

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 66 matching lines @@
 
     EXPECT_EQ(250, viewport->scrollPosition().y());
     EXPECT_EQ(document().getElementById("block2")->layoutObject(),
         scrollAnchor(viewport).anchorObject());
 
     // ScrollableArea::userScroll should clear the anchor.
     viewport->userScroll(ScrollByPrecisePixel, FloatSize(0, 100));
     EXPECT_EQ(nullptr, scrollAnchor(viewport).anchorObject());
 }
 
+TEST_F(ScrollAnchorTest, FractionalOffsetsAreRoundedBeforeComparing)
+{
+    setBodyInnerHTML(
+        "<style> body { height: 1000px } </style>"
+        "<div id='block1' style='height: 50.4px'>abc</div>"
+        "<div id='block2' style='height: 100px'>def</div>");
+
+    ScrollableArea* viewport = layoutViewport();
+    scrollLayoutViewport(DoubleSize(0, 100));
+
+    document().getElementById("block1")->setAttribute(
+        HTMLNames::styleAttr, "height: 50.6px");
+    update();
+
+    EXPECT_EQ(101, viewport->scrollPosition().y());
+}
+
 TEST_F(ScrollAnchorTest, UMAMetricUpdated)
 {
     HistogramTester histogramTester;
     setBodyInnerHTML(
         "<style> body { height: 1000px } div { height: 100px } </style>"
         "<div id='block1'>abc</div>"
         "<div id='block2'>def</div>");
 
     ScrollableArea* viewport = layoutViewport();
 
@@ skipping 195 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));
 }
 
 }