video_coding: Moving video metrics computation to a designated file.

This is the first stage of a general clean-up to test_util. Will try to divide this clean-up to small changes, so it will be easier to review. 
Review URL: http://webrtc-codereview.appspot.com/120004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@466 4adac7df-926f-26a2-2b94-8c16560cd09d

src/modules/video_coding/main/source/video_coding_test.gyp

@@ -37,6 +37,7 @@
         '../test/release_test.h',
         '../test/rtp_player.h',
         '../test/test_util.h',
+        '../test/video_metrics.h',
         '../test/video_source.h',
 
         # sources
@@ -52,6 +53,7 @@
         '../test/rtp_player.cc',
         '../test/test_util.cc',
         '../test/tester_main.cc',
+        '../test/video_metrics.cc',
         '../test/video_rtp_play_mt.cc',
         '../test/video_rtp_play.cc',
         '../test/video_source.cc',