Remove mock_ffmpeg and update media unittests.

media/base/run_all_unittests.cc

Index: media/base/run_all_unittests.cc
diff --git a/media/base/run_all_unittests.cc b/media/base/run_all_unittests.cc
index b715a328b99286174ddecba83883a432fc37ff9d..1ebea6b1099c430698e4dde9b2f8a9e2590ffa0a 100644
--- a/media/base/run_all_unittests.cc
+++ b/media/base/run_all_unittests.cc
@@ -3,7 +3,12 @@
 // found in the LICENSE file.
 
 #include "base/test/test_suite.h"
+#include "media/base/media.h"
 
 int main(int argc, char** argv) {
-  return base::TestSuite(argc, argv).Run();
+  base::TestSuite suite(argc, argv);
+
+  media::InitializeMediaLibraryForTesting();
+
+  return suite.Run();
 }