Add external resize tests

Adds a test that ensures the application is able to trigger frame size
changes via vpx_codec_enc_config_set()

Change-Id: I231c062e533d75c8d63c5f8a5544650117429a63
diff --git a/test/encode_test_driver.h b/test/encode_test_driver.h
index 43faaae..2fb627c 100644
--- a/test/encode_test_driver.h
+++ b/test/encode_test_driver.h
@@ -32,6 +32,10 @@
                                          ::libvpx_test::kTwoPassGood, \
                                          ::libvpx_test::kTwoPassBest)
 
+#define ONE_PASS_TEST_MODES ::testing::Values(::libvpx_test::kRealTime, \
+                                              ::libvpx_test::kOnePassGood, \
+                                              ::libvpx_test::kOnePassBest)
+
 
 // Provides an object to handle the libvpx get_cx_data() iteration pattern
 class CxDataIterator {