ozone: Add atomic initialization path

ui/ozone/platform/drm/ozone_platform_gbm.cc

Index: ui/ozone/platform/drm/ozone_platform_gbm.cc
diff --git a/ui/ozone/platform/drm/ozone_platform_gbm.cc b/ui/ozone/platform/drm/ozone_platform_gbm.cc
index 75f93c586fcef8953f83ea41ac496c84cf691fb4..38b821855c90d24513f5d087d720b5963386f5c5 100644
--- a/ui/ozone/platform/drm/ozone_platform_gbm.cc
+++ b/ui/ozone/platform/drm/ozone_platform_gbm.cc
@@ -89,20 +89,22 @@ class GbmBufferGenerator : public ScanoutBufferGenerator {
 
 class GbmDeviceGenerator : public DrmDeviceGenerator {
  public:
-  GbmDeviceGenerator() {}
+  GbmDeviceGenerator(bool use_atomic) : use_atomic_(use_atomic) {}
   ~GbmDeviceGenerator() override {}
 
   // DrmDeviceGenerator:
   scoped_refptr<DrmDevice> CreateDevice(const base::FilePath& path,
                                         base::File file) override {
     scoped_refptr<DrmDevice> drm = new GbmDevice(path, file.Pass());
-    if (drm->Initialize())
+    if (drm->Initialize(use_atomic_))
       return drm;
 
     return nullptr;
   }
 
  private:
+  bool use_atomic_;
+
   DISALLOW_COPY_AND_ASSIGN(GbmDeviceGenerator);
 };
 
@@ -170,12 +172,14 @@ class OzonePlatformGbm : public OzonePlatform {
   }
 
   void InitializeGPU() override {
+    bool use_atomic = base::CommandLine::ForCurrentProcess()->HasSwitch(
+        switches::kOzoneUseAtomicDrm);
 #if defined(OS_CHROMEOS)
     gpu_lock_.reset(new GpuLock());
 #endif
     gl_api_loader_.reset(new GlApiLoader());
     drm_device_manager_.reset(new DrmDeviceManager(
-        scoped_ptr<DrmDeviceGenerator>(new GbmDeviceGenerator())));
+        scoped_ptr<DrmDeviceGenerator>(new GbmDeviceGenerator(use_atomic))));
     buffer_generator_.reset(new GbmBufferGenerator());
     screen_manager_.reset(new ScreenManager(buffer_generator_.get()));
     if (!surface_factory_ozone_)