Add WARPED_MOTION experiment

Performance gain (REF_MV on by default)
WARPED_MOTION: 1.061%
WARPED_MOTION+MOTION_VAR: 2.917%
MOTION_VAR: 2.337%

Change-Id: I43f742a02cdd43d13ef333a0a15087062ad020ab
diff --git a/av1/common/mvref_common.h b/av1/common/mvref_common.h
index 95fd6ca..e520336 100644
--- a/av1/common/mvref_common.h
+++ b/av1/common/mvref_common.h
@@ -488,6 +488,11 @@
                            int16_t *mode_context);
 #endif  // CONFIG_EXT_INTER
 
+#if CONFIG_WARPED_MOTION
+int findSamples(const AV1_COMMON *cm, MACROBLOCKD *xd, int mi_row, int mi_col,
+                double *pts, double *pts_inref);
+#endif  // CONFIG_WARPED_MOTION
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif