hwc: Add support to query CWB support.

CRs-Fixed: 2607415
Change-Id: I5e0e084d5b25884652e799ac09c558c79c73edd3
diff --git a/composer/hwc_display.h b/composer/hwc_display.h
index 6bcb489..c96fe61 100644
--- a/composer/hwc_display.h
+++ b/composer/hwc_display.h
@@ -409,6 +409,7 @@
       VsyncPeriodChangeTimeline *out_timeline);
 
   HWC2::Error SetDisplayElapseTime(uint64_t time);
+  virtual bool HasReadBackBufferSupport() { return false; }
 
  protected:
   static uint32_t throttling_refresh_rate_;