camera: Drop pending preview for enableZsl shots

If the device support ZSL, drop pending preview buffers to reduce
the chance the rendering preview frames newer than the still frame
during takePicture().

Test: CTS
Bug: 67497723
Change-Id: I5f253a402a6302d31777ad4ca2878ef0d0d1ae44
Merged-In: I5f253a402a6302d31777ad4ca2878ef0d0d1ae44
diff --git a/services/camera/libcameraservice/device3/Camera3Device.h b/services/camera/libcameraservice/device3/Camera3Device.h
index fbbbd08..081af19 100644
--- a/services/camera/libcameraservice/device3/Camera3Device.h
+++ b/services/camera/libcameraservice/device3/Camera3Device.h
@@ -178,6 +178,12 @@
      */
     status_t setConsumerSurfaces(int streamId, const std::vector<sp<Surface>>& consumers) override;
 
+    /**
+     * Drop buffers for stream of streamId if dropping is true. If dropping is false, do not
+     * drop buffers for stream of streamId.
+     */
+    status_t dropStreamBuffers(bool dropping, int streamId) override;
+
   private:
 
     // internal typedefs