Revert "drm_hwcomposer: remove compositor interface"

This reverts commit 7912438911de042dc035cf1ea39daaf4e56bf9f3.

For now until we can get back to a stable SF/compositor.

Change-Id: I2ba7cab4f1cccfe44b3d35fb18c7784125e88fd6
diff --git a/drmcomposition.h b/drmcomposition.h
index 69bf6d9..06af71d 100644
--- a/drmcomposition.h
+++ b/drmcomposition.h
@@ -17,6 +17,7 @@
 #ifndef ANDROID_DRM_COMPOSITION_H_
 #define ANDROID_DRM_COMPOSITION_H_
 
+#include "compositor.h"
 #include "drm_hwcomposer.h"
 #include "drmdisplaycomposition.h"
 #include "drmplane.h"
@@ -31,15 +32,15 @@
 
 namespace android {
 
-class DrmComposition {
+class DrmComposition : public Composition {
  public:
   DrmComposition(DrmResources *drm, Importer *importer);
   ~DrmComposition();
 
-  int Init();
+  virtual int Init();
 
-  unsigned GetRemainingLayers(int display, unsigned num_needed) const;
-  int AddLayer(int display, hwc_layer_1_t *layer, hwc_drm_bo_t *bo);
+  virtual unsigned GetRemainingLayers(int display, unsigned num_needed) const;
+  virtual int AddLayer(int display, hwc_layer_1_t *layer, hwc_drm_bo_t *bo);
   int AddDpmsMode(int display, uint32_t dpms_mode);
 
   int DisableUnusedPlanes();