power save blocker: Don't try to block power saving in headless mode

device/power_save_blocker/power_save_blocker_x11.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 <X11/Xlib.h>
 #include <X11/extensions/dpms.h>
 #include <X11/extensions/scrnsaver.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 14 matching lines @@
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/singleton.h"
 #include "base/nix/xdg_util.h"
 #include "base/synchronization/lock.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
 #include "dbus/object_path.h"
 #include "dbus/object_proxy.h"
+#include "ui/gfx/switches.h"
 #include "ui/gfx/x/x11_types.h"
 
 namespace {
 
 enum DBusAPI {
   NO_API,           // Disable. No supported API available.
   GNOME_API,        // Use the GNOME API. (Supports more features.)
   FREEDESKTOP_API,  // Use the FreeDesktop API, for KDE4, KDE5, and XFCE.
 };
 
@@ skipping 434 matching lines @@
     const std::string& description,
     scoped_refptr<base::SequencedTaskRunner> ui_task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> blocking_task_runner)
     : delegate_(new Delegate(type,
                              description,
                              false /* freedesktop_only */,
                              ui_task_runner,
                              blocking_task_runner)),
       ui_task_runner_(ui_task_runner),
       blocking_task_runner_(blocking_task_runner) {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kHeadless))

[hashimoto, 2017/01/17 02:08:12]

1. Instead of adding if to the ctor and the dtor, please modify
PowerSaveBlocker::Delegate::SelectAPI() above to return NO_API
2. I'm not familiar with base::nix::GetDesktopEnvironment(), but shouldn't it
detect it when X11 is not available?
3. Do we really want to always disable poser save blocker when running headless?

[Sami, 2017/01/17 13:44:29]

Good idea, done. (Note that I had to do the same to the X screensaver related
code.)
Looks like it doesn't check for X11 as such, which I think is correct since not
all the detected environments actually require X11.
I believe so. There's no API we could use to control power saving so the blocker
can't really do anything in the first place.

+    return;
   delegate_->Init();
 
   if (type == kPowerSaveBlockPreventDisplaySleep) {
     freedesktop_suspend_delegate_ = new Delegate(
         kPowerSaveBlockPreventAppSuspension, description,
         true /* freedesktop_only */, ui_task_runner, blocking_task_runner);
     freedesktop_suspend_delegate_->Init();
   }
 }
 
 PowerSaveBlocker::~PowerSaveBlocker() {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kHeadless))
+    return;
   delegate_->CleanUp();
   if (freedesktop_suspend_delegate_)
     freedesktop_suspend_delegate_->CleanUp();
 }
 
 }  // namespace device