Consolidate HWC display context design.

BZ: 99199

Define IDisplayContext interface for committing  metadata and contents of all HWC layers to hardware
using this interface.

This consolidation will make it easier to switch to a different commit method as all implementations
are in the same file.

Change-Id: I4c9b2aa63066c1591f0d24c5b429ff2ea77a9673
Signed-off-by: Andy Qiu <junhai.qiu@intel.com>
Reviewed-on: http://android.intel.com:8080/100814
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>
diff --git a/include/VirtualDevice.h b/include/VirtualDevice.h
index 4fe4ed1..30138ca 100644
--- a/include/VirtualDevice.h
+++ b/include/VirtualDevice.h
@@ -46,8 +46,7 @@
     virtual bool prePrepare(hwc_display_contents_1_t *display);
     virtual bool prepare(hwc_display_contents_1_t *display);
     virtual bool commit(hwc_display_contents_1_t *display,
-                          void* context,
-                          int& count) = 0;
+                          IDisplayContext *context);
 
     virtual bool vsyncControl(int enabled);
     virtual bool blank(int blank);