Remove mock_ffmpeg and update media unittests.

media/base/media_win.cc

Index: media/base/media_win.cc
diff --git a/media/base/media_win.cc b/media/base/media_win.cc
index a58d977fe6b99dd5512a09cdcfbccd4568587ee7..9462c0281f34cd74442c8e3ee08f1943410f5acb 100644
--- a/media/base/media_win.cc
+++ b/media/base/media_win.cc
@@ -78,6 +78,12 @@ bool InitializeMediaLibrary(const FilePath& base_path) {
   return g_media_library_is_initialized;
 }
 
+void InitializeMediaLibraryForTesting() {
+  FilePath file_path;
+  CHECK(PathService::Get(base::DIR_EXE, &file_path));
+  CHECK(InitializeMediaLibrary(file_path));
+}
+
 bool IsMediaLibraryInitialized() {
   return g_media_library_is_initialized;
 }