Switch DRM platform to using a separate thread

ui/ozone/platform/drm/gpu/drm_device_manager.h

Index: ui/ozone/platform/drm/gpu/drm_device_manager.h
diff --git a/ui/ozone/platform/drm/gpu/drm_device_manager.h b/ui/ozone/platform/drm/gpu/drm_device_manager.h
index 34fe61335d62cb1bb9165d8ef3d7ea0467130f68..72b9b9ffd819fd25939a478b9ae93c3b07ab964a 100644
--- a/ui/ozone/platform/drm/gpu/drm_device_manager.h
+++ b/ui/ozone/platform/drm/gpu/drm_device_manager.h
@@ -10,15 +10,12 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/synchronization/lock.h"
-#include "base/threading/thread_checker.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/ozone/ozone_export.h"
 
 namespace base {
 class FilePath;
 struct FileDescriptor;
-class SingleThreadTaskRunner;
 }
 
 namespace ui {
@@ -30,8 +27,6 @@ typedef std::vector<scoped_refptr<DrmDevice>> DrmDeviceVector;
 
 // Tracks the mapping between widgets and the DRM devices used to allocate
 // buffers for the window represented by the widget.
-// Note: All calls are protected by a lock since
-// GetDrmDevice(gfx::AcceleratedWidget) may be called on the IO thread.
 class OZONE_EXPORT DrmDeviceManager {
  public:
   DrmDeviceManager(scoped_ptr<DrmDeviceGenerator> drm_device_generator);
@@ -41,9 +36,6 @@ class OZONE_EXPORT DrmDeviceManager {
   bool AddDrmDevice(const base::FilePath& path, const base::FileDescriptor& fd);
   void RemoveDrmDevice(const base::FilePath& path);
 
-  void InitializeIOTaskRunner(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
-
   // Updates the device associated with |widget|.
   void UpdateDrmDevice(gfx::AcceleratedWidget widget,
                        const scoped_refptr<DrmDevice>& device);
@@ -58,14 +50,8 @@ class OZONE_EXPORT DrmDeviceManager {
   const DrmDeviceVector& GetDrmDevices() const;
 
  private:
-  // With the exception of GetDrmDevice() all functions must be called on GPU
-  // main.
-  base::ThreadChecker thread_checker_;
-
   scoped_ptr<DrmDeviceGenerator> drm_device_generator_;
 
-  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
-
   DrmDeviceVector devices_;
 
   std::map<gfx::AcceleratedWidget, scoped_refptr<DrmDevice>> drm_device_map_;
@@ -78,10 +64,6 @@ class OZONE_EXPORT DrmDeviceManager {
   // display; ie: when in headless mode).
   scoped_refptr<DrmDevice> primary_device_;
 
-  // This class is accessed from the main thread and the IO thread. This lock
-  // protects access to the device map.
-  base::Lock lock_;
-
   DISALLOW_COPY_AND_ASSIGN(DrmDeviceManager);
 };