No more parameterized tests linkage warnings.

[ Merge of http://go/wvgerrit/85153 ]

Issues addressed in this CL:
1)  Linkage warnings in g++
2)  Inconsistent `override` with clang++
3)  Test variable names

Some of our tests use types defined in test-local anonymous namespace.  For
our tests setup, this does not cause any linkage issues; however, g++ produces
warnings about it.

The options were to suppress it with `-Wno-subobject-linkage`, or to change
the tests to avoid even the potential of a linkage error.

There were additional warnings showing up about the use of `override` on
derived mock classes.  The solution was simply to remove the `override`
qualifier on `MockFile`'s destructor.

Some of the test data variables were using snake_case, here I switched it to
kConstantCamelCase.

Bug: 139808919
Test: Compiling with gcc, Linux unittests and Android unittests
Change-Id: Ic3f82a6db7fad990ffe49186914084b039ec8a14

libwvdrmengine/cdm/core/test/initialization_data_unittest.cpp

@@ -442,6 +442,8 @@ std::string InsertHlsAttributeInList(const std::string key,
          "=" + kHlsTestValue2;
 }
 
+}  // namespace
+
 struct HlsInitDataVariant {
   HlsInitDataVariant(CdmHlsMethod method, const std::string& provider,
                      const std::string& content_id, const std::string& key_id,
@@ -499,7 +501,6 @@ class HlsParseTest : public ::testing::TestWithParam<HlsAttributeVariant> {};
 
 class HlsTest : public ::testing::Test {};
 
-}  // namespace
 
 TEST_F(InitializationDataTest, BadType) {
   InitializationData init_data("bad", kWidevinePssh);