Add HeadlessFocusClient to fix document.hasFocus() issues.

headless/lib/browser/headless_browser_impl_aura.cc

Index: headless/lib/browser/headless_browser_impl_aura.cc
diff --git a/headless/lib/browser/headless_browser_impl_aura.cc b/headless/lib/browser/headless_browser_impl_aura.cc
index 9237e347112052370d506943b67c40ee6c92cf23..e9e27bc13856cd9e3b376ef9290228a5ad44c84e 100644
--- a/headless/lib/browser/headless_browser_impl_aura.cc
+++ b/headless/lib/browser/headless_browser_impl_aura.cc
@@ -7,7 +7,9 @@
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "headless/lib/browser/headless_screen.h"
+#include "ui/aura/client/focus_client.h"
 #include "ui/aura/env.h"
+#include "ui/aura/test/test_focus_client.h"
 #include "ui/aura/window.h"
 #include "ui/display/screen.h"
 #include "ui/events/devices/device_data_manager.h"
@@ -29,6 +31,10 @@ void HeadlessBrowserImpl::PlatformCreateWindow() {
   window_tree_host_->InitHost();
   window_tree_host_->window()->Show();
   window_tree_host_->SetParentWindow(window_tree_host_->window());
+
+  focus_client_.reset(new aura::test::TestFocusClient());
+  aura::client::SetFocusClient(window_tree_host_->window(),
+                               focus_client_.get());
 }
 
 void HeadlessBrowserImpl::PlatformInitializeWebContents(