media: Add unittest for MojoRenderer{Impl|Service}

media/base/mock_filters.cc

Index: media/base/mock_filters.cc
diff --git a/media/base/mock_filters.cc b/media/base/mock_filters.cc
index cff598abe54c735b8314361ed230144b23e0b649..0a7536bad534a13527034d8dd4f443c5c55b3717 100644
--- a/media/base/mock_filters.cc
+++ b/media/base/mock_filters.cc
@@ -135,7 +135,11 @@ MockCdmContext::MockCdmContext() {}
 MockCdmContext::~MockCdmContext() {}
 
 int MockCdmContext::GetCdmId() const {
-  return CdmContext::kInvalidCdmId;
+  return cdm_id_;
+}
+
+void MockCdmContext::set_cdm_id(int cdm_id) {
+  cdm_id_ = cdm_id;
 }
 
 }  // namespace media