Implement findAnchor and computeRelativeOffset in ScrollAnchor.

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

Index: third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp
diff --git a/third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp b/third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp
index 26262fa8ab13ed3a4244d3cdb5119afce1e0a3d5..8faf1851b233a40f5cc8f2b3b0fd3269d64b0bec 100644
--- a/third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp
+++ b/third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp
@@ -19,8 +19,16 @@ class ScrollAnchorTest : public RenderingTest {
 
 TEST_F(ScrollAnchorTest, Basic)
 {
-    ScrollAnchor scrollAnchor(document().view()->layoutViewportScrollableArea());
-    scrollAnchor.clear();
-    EXPECT_EQ(nullptr, scrollAnchor.anchorObject());
+    setBodyInnerHTML(
+        "<style> body { height: 1000px } div { height: 100px } </style>"
+        "<div id='block1'>abc</div>"
+        "<div id='block2'>def</div>");
+
+    ScrollableArea* viewport = document().view()->layoutViewportScrollableArea();
+    viewport->scrollBy(DoubleSize(0, 150), UserScroll);
+    document().getElementById("block1")->setAttribute(HTMLNames::styleAttr, "height: 200px");
+    document().view()->updateAllLifecyclePhases();
+    EXPECT_EQ(250, viewport->scrollPosition().y());
 }
+
 }