Implement a runtime headless mode for Linux

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 c1647257fd3e46fe2578c035204dac74c86e54bf..aad7e85f497a66e92cb19638d77ba7c8888413b9 100644
--- a/headless/lib/browser/headless_browser_impl.cc
+++ b/headless/lib/browser/headless_browser_impl.cc
@@ -19,9 +19,10 @@
 #include "headless/lib/browser/headless_browser_main_parts.h"
 #include "headless/lib/browser/headless_web_contents_impl.h"
 #include "headless/lib/browser/headless_window_parenting_client.h"
+#include "headless/lib/browser/headless_window_tree_host.h"
 #include "headless/lib/headless_content_main_delegate.h"
 #include "ui/aura/env.h"
-#include "ui/aura/window_tree_host.h"
+#include "ui/events/devices/device_data_manager.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace headless {
@@ -119,8 +120,10 @@ void HeadlessBrowserImpl::set_browser_main_parts(
 
 void HeadlessBrowserImpl::RunOnStartCallback() {
   DCHECK(aura::Env::GetInstance());
+  ui::DeviceDataManager::CreateInstance();
+
   window_tree_host_.reset(
-      aura::WindowTreeHost::Create(gfx::Rect(options()->window_size)));
+      new HeadlessWindowTreeHost(gfx::Rect(options()->window_size)));

[Eric Seckler, 2016/11/28 15:51:48]

I suspect that this is the reason for the screenshots not coming back, but I
can't really tell what's missing in HeadlessWindowTreeHost either :(

[Sami, 2016/11/28 18:00:36]

No worries, turns out the problem was that we need to return false from
ShouldCreateGpuCompositorFrameSink().

   window_tree_host_->InitHost();
 
   window_parenting_client_.reset(