Add service unittest for WakeLockServiceImpl.

device/power_save_blocker/power_save_blocker_x11.cc

Index: device/power_save_blocker/power_save_blocker_x11.cc
diff --git a/device/power_save_blocker/power_save_blocker_x11.cc b/device/power_save_blocker/power_save_blocker_x11.cc
index 8c96590eaab5f29bf88ce0662560af775c9dc893..3a77287647b1d7fa0440202d1cd5e807e8bd8e3f 100644
--- a/device/power_save_blocker/power_save_blocker_x11.cc
+++ b/device/power_save_blocker/power_save_blocker_x11.cc
@@ -441,6 +441,10 @@ bool PowerSaveBlocker::Delegate::XSSAvailable() {
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kHeadless))
     return false;
   XDisplay* display = gfx::GetXDisplay();
+  // In service_unittests context, XDisplay is not well initialized. passing a
+  // nullptr to XScreenSaverQueryExtension() will cause crash.

[scottmg, 2017/05/17 16:00:32]

nit; if we keep this, a more natural phrasing:

  // In service_unittests, XDisplay is not initialized. Passing a nullptr to
  // XScreenSaverQueryExtension() will cause a crash.

[ke.he, 2017/05/19 03:46:51]

Done.

+  if (!display)
+    return false;

[scottmg, 2017/05/17 16:00:32]

Could you recheck this? At the top of WakeLockServiceImplTest::SetUp(), I added

DCHECK(gfx::InitializeThreadedX11());

(plus BUILD and #include) and all the tests seem to pass locally for me.

I ran as `python testing/xvfb.py out/Debug/service_unittests
--gtest_filter=WakeLockServiceImplTest.*`.

   int dummy;

[scottmg, 2017/05/17 16:00:32]

nit; Add a blank line before int dummy;.

[ke.he, 2017/05/19 03:46:51]

Done.

   int major;
   int minor;