Link sidebar "location" heading to top of page

This makes it easy, when you are scrolled far down in a page, to jump
back to the top.

src/test/rustdoc-gui/sidebar.goml

@@ -22,6 +22,13 @@ click: "#structs + .item-table .item-left > a"
 assert-count: (".sidebar .location", 2)
 // We check that there is no crate listed outside of the top level.
 assert-false: ".sidebar-elems > .crate"
+
+click: ".sidebar-links a"
+assert-property: ("html", {"scrollTop": "389"})
+
+click: ".sidebar h2.location"
+assert-property: ("html", {"scrollTop": "0"})
+
 // We now go back to the crate page to click on the "lib2" crate link.
 goto: file://|DOC_PATH|/test_docs/index.html
 click: ".sidebar-elems .crate > ul > li:first-child > a"