Add HeadlessFocusClient to fix document.hasFocus() issues.

headless/lib/browser/headless_web_contents_impl.cc

Index: headless/lib/browser/headless_web_contents_impl.cc
diff --git a/headless/lib/browser/headless_web_contents_impl.cc b/headless/lib/browser/headless_web_contents_impl.cc
index 9d4b7add3323b2db989e49f990c62d79346bf0ae..2a2f780bc13412a13766c7f2f4929d851a0a1a11 100644
--- a/headless/lib/browser/headless_web_contents_impl.cc
+++ b/headless/lib/browser/headless_web_contents_impl.cc
@@ -21,6 +21,8 @@
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
+#include "content/public/browser/render_widget_host.h"
+#include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_delegate.h"
 #include "content/public/common/bindings_policy.h"
@@ -97,6 +99,10 @@ class HeadlessWebContentsImpl::Delegate : public content::WebContentsDelegate {
                                             security_style_explanations);
   }
 
+  void ActivateContents(content::WebContents* contents) override {
+    contents->GetTopLevelRenderWidgetHostView()->GetRenderWidgetHost()->Focus();

[Eric Seckler, 2017/02/21 09:28:02]

Hm, the content shell does:
  contents->GetRenderViewHost()->GetWidget()->Focus();

Which probably amounts to the same, but I'm not sure. Do you have a rationale
for calling focus() on the top-level RWH rather than the current view's RWH? :)

[irisu, 2017/02/22 05:34:35]

No, I don't. Done.

+  }
+
  private:
   HeadlessBrowserContextImpl* browser_context_;  // Not owned.
   DISALLOW_COPY_AND_ASSIGN(Delegate);
@@ -181,6 +187,7 @@ bool HeadlessWebContentsImpl::OpenURL(const GURL& url) {
       ui::PAGE_TRANSITION_TYPED | ui::PAGE_TRANSITION_FROM_ADDRESS_BAR);
   web_contents_->GetController().LoadURLWithParams(params);
   web_contents_->Focus();
+  web_contents_delegate_->ActivateContents(web_contents_.get());

[Eric Seckler, 2017/02/21 09:28:02]

Ah, okay. I thought ActivateContents would be called when required by the
content layer. Seems that's not true :)

I looked into why the above web_contents_->Focus() call doesn't seem to work. It
ends up in RenderWidgetHostViewAura::Focus() here:

https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_wid...

Turns out, that doesn't have any effect because we currently don't set a
aura::client::FocusClient. Maybe the better solution is to set one. The content
shell uses a TestFocusClient, which is probably also fine for us, at least for
the moment:

https://cs.chromium.org/chromium/src/content/shell/browser/shell_platform_dat...

We can probably set it when we initialize the WindowTreeHost (on its root
window) in HeadlessBrowserImpl::PlatformCreateWindow().

The change to ActivateContents() is probably useful nevertheless, we just don't
have to call it from here then.

[irisu, 2017/02/22 05:34:35]

Done. I'm getting a presubmit warning for using TestFocusClient in production,
but I'm assuming that's fine.
"You might be calling functions intended only for testing from
production code.  It is OK to ignore this warning if you know what
you are doing, as the heuristics used to detect the situation are
not perfect.  The commit queue will not block on this warning."

[Eric Seckler, 2017/02/22 09:00:03]

Yeah, it's a reasonable warning, but given that the TestFocusClient is also used
by content_shell, I'd consider ignoring it appropriate in this case :)

[Eric Seckler, 2017/02/22 10:28:59]

Seems like we'll also have to add a build dependency on the test lib
(//ui/aura:test_support):

[4652/4655] LINK ./chrome
FAILED: chrome [..]
../../headless/lib/browser/headless_browser_impl_aura.cc:35: error: undefined
reference to 'aura::test::TestFocusClient::TestFocusClient()'

The alternative would be to try and convince aura owners that TestFocusClient
(maybe renamed to e.g. FakeFocusClient) should live in /ui/aura, and not the
test support library. Or we just go ahead and build our own one now.

   return true;
 }