cosmetics: normalize include guards

use the recommended format [1] of:
<PROJECT>_<PATH>_<FILE>_H_

[1] https://google.github.io/styleguide/cppguide.html#The__define_Guard
"All header files should have #define guards to prevent multiple
inclusion. The format of the symbol name should be
<PROJECT>_<PATH>_<FILE>_H_."

Change-Id: I00a0595fc2a5fc736ab6ff3215727d6db05b10e1
diff --git a/test/video_source.h b/test/video_source.h
index dc39b5a..3c1c5e5 100644
--- a/test/video_source.h
+++ b/test/video_source.h
@@ -8,8 +8,8 @@
  * Media Patent License 1.0 was not distributed with this source code in the
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
-#ifndef TEST_VIDEO_SOURCE_H_
-#define TEST_VIDEO_SOURCE_H_
+#ifndef AOM_TEST_VIDEO_SOURCE_H_
+#define AOM_TEST_VIDEO_SOURCE_H_
 
 #if defined(_WIN32)
 #undef NOMINMAX
@@ -256,4 +256,4 @@
 
 }  // namespace libaom_test
 
-#endif  // TEST_VIDEO_SOURCE_H_
+#endif  // AOM_TEST_VIDEO_SOURCE_H_