Adds 'virtual' and 'const' modifiers to methods in wv_cas_ecm.

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Expose header files under export/exported_root/util in media_cas_packager_sdk because util::Status is used in wv_cas_ecm.h

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=218632176

BUILD

@@ -16,6 +16,7 @@ pkg_tar(
     files = [
         "//example:binary_release_files",
         "//media_cas_packager_sdk/public:binary_release_files",
+        "//util:binary_release_files",
     ],
     mode = "0644",
 )