Changing all PSNR/SSIM calculations to use libyuv.

Removed old PSNR/SSIM implementations in:
* test/testsupport/metrics/video_metrics.cc
* src/modules/video_coding/codecs/test_framework/test.cc
The functions in video_metrics.cc is now using code in libyuv instead. Old code in test.cc is using the same functions.
The code for video_metrics.h had to be moved into a separate GYP file to avoid circular dependency error on Mac (see issue 160 for more details). The reason for this is that libyuv's unittest target depends on test_support_main.

BUG=
TEST=metrics_unittests in Debug+Release on Linux, Mac and Windows.

Review URL: http://webrtc-codereview.appspot.com/333025

git-svn-id: http://webrtc.googlecode.com/svn/trunk@1325 4adac7df-926f-26a2-2b94-8c16560cd09d

test/test.gyp

@@ -43,8 +43,6 @@
         'testsupport/frame_writer.cc',
         'testsupport/packet_reader.h',
         'testsupport/packet_reader.cc',
-        'testsupport/metrics/video_metrics.h',
-        'testsupport/metrics/video_metrics.cc',
         'testsupport/mock/mock_frame_reader.h',
         'testsupport/mock/mock_frame_writer.h',
       ],
@@ -74,7 +72,6 @@
         'testsupport/frame_reader_unittest.cc',
         'testsupport/frame_writer_unittest.cc',
         'testsupport/packet_reader_unittest.cc',
-        'testsupport/metrics/video_metrics_unittest.cc',
       ],
     },
   ],