Camera: implement buffer managment API

Test: compile
Bug: 109829698
Change-Id: I3d95792282da52db9db6fd6a086bbd7b3ff9dca9
diff --git a/services/camera/libcameraservice/device3/Camera3StreamInterface.h b/services/camera/libcameraservice/device3/Camera3StreamInterface.h
index 5758ac8..866b722 100644
--- a/services/camera/libcameraservice/device3/Camera3StreamInterface.h
+++ b/services/camera/libcameraservice/device3/Camera3StreamInterface.h
@@ -289,6 +289,11 @@
      */
     virtual bool     hasOutstandingBuffers() const = 0;
 
+    /**
+     * Get number of buffers currently handed out to HAL
+     */
+    virtual size_t   getOutstandingBuffersCount() const = 0;
+
     enum {
         TIMEOUT_NEVER = -1
     };