headless: Implement screenshot capturing

headless/lib/browser/headless_browser_impl.cc

Index: headless/lib/browser/headless_browser_impl.cc
diff --git a/headless/lib/browser/headless_browser_impl.cc b/headless/lib/browser/headless_browser_impl.cc
index 3b19175a2b5787794ac0db54cdd4bc5607b32202..f34849f3d993a02c39de908d65cf6856063cab99 100644
--- a/headless/lib/browser/headless_browser_impl.cc
+++ b/headless/lib/browser/headless_browser_impl.cc
@@ -4,6 +4,8 @@
 
 #include "headless/lib/browser/headless_browser_impl.h"
 
+#include <vector>

[Sami, 2016/06/02 14:22:19]

unused?

[Eric Seckler, 2016/06/02 17:56:31]

I added this b/c GetAllWebContents() uses std::vector and my cpplint complained
:P

I can get rid of it and look at all the linting issues in a separate commit if
that's more sensible.

[Sami, 2016/06/02 18:01:33]

Oh I see. Fine to fix it here then.

+
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/public/app/content_main.h"
@@ -87,7 +89,10 @@ void HeadlessBrowserImpl::set_browser_main_parts(
 
 void HeadlessBrowserImpl::RunOnStartCallback() {
   DCHECK(aura::Env::GetInstance());
-  window_tree_host_.reset(aura::WindowTreeHost::Create(gfx::Rect()));
+  // TODO(eseckler): allow configuration of window (viewport) size by embedder
+  const gfx::Size kDefaultSize(800, 600);
+  window_tree_host_.reset(
+      aura::WindowTreeHost::Create(gfx::Rect(kDefaultSize)));
   window_tree_host_->InitHost();
 
   window_tree_client_.reset(