Create an interactive site-per-process browsertest class and move DocumentHasFocus there.

content/public/test/browser_test_utils.cc

Index: content/public/test/browser_test_utils.cc
diff --git a/content/public/test/browser_test_utils.cc b/content/public/test/browser_test_utils.cc
index fac8957dbfd8e28c7518cbcb49e8401e6c04cdec..70a06cc2a4bed7db75da0e123b3c312ee86e9d40 100644
--- a/content/public/test/browser_test_utils.cc
+++ b/content/public/test/browser_test_utils.cc
@@ -24,6 +24,8 @@
 #include "content/browser/accessibility/accessibility_mode_helper.h"
 #include "content/browser/accessibility/browser_accessibility.h"
 #include "content/browser/accessibility/browser_accessibility_manager.h"
+#include "content/browser/frame_host/frame_tree_node.h"
+#include "content/browser/frame_host/render_frame_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/browser/web_contents/web_contents_view.h"
@@ -744,6 +746,13 @@ bool FrameHasSourceUrl(const GURL& url, RenderFrameHost* frame) {
   return frame->GetLastCommittedURL() == url;
 }
 
+RenderFrameHost* ChildFrameAt(RenderFrameHost* frame, size_t index) {
+  RenderFrameHostImpl* rfh = static_cast<RenderFrameHostImpl*>(frame);
+  if (index >= rfh->frame_tree_node()->child_count())
+    return nullptr;
+  return rfh->frame_tree_node()->child_at(index)->current_frame_host();
+}
+
 bool ExecuteWebUIResourceTest(WebContents* web_contents,
                               const std::vector<int>& js_resource_ids) {
   // Inject WebUI test runner script first prior to other scripts required to