Implement a runtime headless mode for Linux

ui/aura/env.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/env.h"
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread_local.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/env_observer.h"
 #include "ui/aura/input_state_lookup.h"
 #include "ui/aura/mus/window_port_mus.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_observer.h"
 #include "ui/aura/window_port_local.h"
 #include "ui/events/event_target_iterator.h"
 #include "ui/events/platform/platform_event_source.h"
+#include "ui/gfx/switches.h"
 
 #if defined(USE_OZONE)
 #include "ui/ozone/public/ozone_platform.h"
 #endif
 
 namespace aura {
 
 namespace {
 
 // Env is thread local so that aura may be used on multiple threads.
 base::LazyInstance<base::ThreadLocalPointer<Env> >::Leaky lazy_tls_ptr =
     LAZY_INSTANCE_INITIALIZER;
 
 // Returns true if running inside of mus. Checks for mojo specific flag.
 bool RunningInsideMus() {
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       "primordial-pipe-token");
 }
 
+bool RunningInHeadlessMode() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kHeadless);
+}
+
 }  // namespace
 
 // Observes destruction and changes of the FocusClient for a window.
 // ActiveFocusClientWindowObserver is created for the window the FocusClient is
 // associated with.
 class Env::ActiveFocusClientWindowObserver : public WindowObserver {
  public:
   explicit ActiveFocusClientWindowObserver(Window* window) : window_(window) {
     window_->AddObserver(this);
   }
@@ skipping 113 matching lines @@
 
 void Env::Init() {
   if (RunningInsideMus())
     return;
 #if defined(USE_OZONE)
   // The ozone platform can provide its own event source. So initialize the
   // platform before creating the default event source. If running inside mus
   // let the mus process initialize ozone instead.
   ui::OzonePlatform::InitializeForUI();
 #endif
+  if (RunningInHeadlessMode())

[sky, 2016/12/06 14:27:31]

Would it make more sense for a headless PlatformEventsource?

[Sami, 2016/12/07 11:51:26]

Great idea! Done.

+    return;
   if (!ui::PlatformEventSource::GetInstance())
     event_source_ = ui::PlatformEventSource::CreateDefault();
 }
 
 void Env::NotifyWindowInitialized(Window* window) {
   for (EnvObserver& observer : observers_)
     observer.OnWindowInitialized(window);
 }
 
 void Env::NotifyHostInitialized(WindowTreeHost* host) {
@@ skipping 24 matching lines @@
 std::unique_ptr<ui::EventTargetIterator> Env::GetChildIterator() const {
   return nullptr;
 }
 
 ui::EventTargeter* Env::GetEventTargeter() {
   NOTREACHED();
   return NULL;
 }
 
 }  // namespace aura