test(chrome): compare the facts both hosts derive from one DOM

The existing parity harness hand-authors the facts on both sides, so it proves
that given identical facts both hosts select identical candidates, and says
nothing about the two code paths that derive those facts from a real page. Four
divergences lived in that blind spot and it passed throughout.

This drives one real page and compares clickable, enabled, editable, scrollable
and positiveBounds element by element, plus the element sets themselves, which
is what catches a host that omits html or includes head. Reverting any of the
four fixes makes it fail naming the element and the fact.

Claude-Session: https://claude.ai/code/session_01A5KmftdEJ49A9z5mF5ESrX

internal/driver/chrome/testdata/fact-parity.html

@@ -0,0 +1,72 @@
+<!doctype html>
+<html id="page">
+  <head id="page-head">
+    <meta id="page-charset" charset="utf-8" />
+    <title id="page-title">fact parity</title>
+    <style id="page-style">
+      :root {
+        --frame-w: 420px;
+        --frame-h: 640px;
+      }
+      body {
+        margin: 0;
+      }
+      #scroller {
+        width: 320px;
+        height: 120px;
+        overflow: auto;
+      }
+      #scroller-content {
+        height: 600px;
+      }
+      #sideways {
+        width: 320px;
+        height: 40px;
+        overflow: auto;
+      }
+      #sideways-content {
+        width: 900px;
+        height: 20px;
+      }
+      #fits {
+        width: 320px;
+        height: 120px;
+        overflow: auto;
+      }
+      #fits-content {
+        height: 40px;
+      }
+      #collapsed {
+        display: none;
+      }
+      #filler {
+        height: 900px;
+      }
+    </style>
+  </head>
+  <body id="page-body">
+    <button id="save">save</button>
+    <button id="cancel" disabled>cancel</button>
+    <a id="link" href="#detail">detail</a>
+    <select id="choice">
+      <option id="choice-first">first</option>
+    </select>
+    <input id="amount" type="text" value="10" />
+    <input id="agree" type="checkbox" />
+    <textarea id="notes"></textarea>
+    <div id="bio" contenteditable="true">bio</div>
+    <div id="menu" role="button">menu</div>
+    <div id="attribute-click" onclick="void 0">attribute click</div>
+    <div id="delegating-root">delegating root</div>
+    <div id="plain">plain</div>
+    <div id="edit-text-field" class="EditTextField">styled</div>
+    <span id="collapsed">collapsed</span>
+    <div id="scroller"><div id="scroller-content"></div></div>
+    <div id="sideways"><div id="sideways-content"></div></div>
+    <div id="fits"><div id="fits-content"></div></div>
+    <div id="filler"></div>
+    <script id="page-script">
+      document.getElementById("delegating-root").onclick = function () {};
+    </script>
+  </body>
+</html>