Add HeadlessFocusClient to fix document.hasFocus() issues.

headless/lib/browser/headless_browser_impl.h

Index: headless/lib/browser/headless_browser_impl.h
diff --git a/headless/lib/browser/headless_browser_impl.h b/headless/lib/browser/headless_browser_impl.h
index e622227f65b5f0e13e89224f3cf8d7fa4dc6338b..864e49c1c17cc666a7ed5a9ee757e8ffb256c9b6 100644
--- a/headless/lib/browser/headless_browser_impl.h
+++ b/headless/lib/browser/headless_browser_impl.h
@@ -19,6 +19,12 @@
 
 #if defined(USE_AURA)
 #include "headless/lib/browser/headless_window_tree_host.h"
+
+namespace aura {
+namespace client {
+class FocusClient;
+}
+}
 #endif
 
 namespace headless {
@@ -81,7 +87,9 @@ class HeadlessBrowserImpl : public HeadlessBrowser {
   // is used for all web contents. We should probably use one
   // window per web contents, but additional investigation is needed.
   std::unique_ptr<HeadlessWindowTreeHost> window_tree_host_;
+  std::unique_ptr<aura::client::FocusClient> focus_client_;
 #endif
+
   base::Callback<void(HeadlessBrowser*)> on_start_callback_;
   HeadlessBrowser::Options options_;
   HeadlessBrowserMainParts* browser_main_parts_;  // Not owned.