Part 5.1: Is policy list subsumed under subsuming policy?

third_party/WebKit/Source/core/frame/csp/MediaListDirective.h

Index: third_party/WebKit/Source/core/frame/csp/MediaListDirective.h
diff --git a/third_party/WebKit/Source/core/frame/csp/MediaListDirective.h b/third_party/WebKit/Source/core/frame/csp/MediaListDirective.h
index d6c67217476000e196ba6e546211afb80ff0d8a9..c9e5cbf7b9e7668216458e525fb87904509b2b18 100644
--- a/third_party/WebKit/Source/core/frame/csp/MediaListDirective.h
+++ b/third_party/WebKit/Source/core/frame/csp/MediaListDirective.h
@@ -14,7 +14,7 @@ namespace blink {
 
 class ContentSecurityPolicy;
 
-class MediaListDirective final : public CSPDirective {
+class CORE_EXPORT MediaListDirective final : public CSPDirective {
   WTF_MAKE_NONCOPYABLE(MediaListDirective);
 
  public:
@@ -23,9 +23,20 @@ class MediaListDirective final : public CSPDirective {
                      ContentSecurityPolicy*);
   bool allows(const String& type);
 
+  // The algorothm is described more extensively here:
+  // https://w3c.github.io/webappsec-csp/embedded/#subsume-policy.
+  bool subsumes(const std::vector<MediaListDirective*>& other);
+
  private:
+  FRIEND_TEST_ALL_PREFIXES(MediaListDirectiveTest, GetIntersect);
+  FRIEND_TEST_ALL_PREFIXES(MediaListDirectiveTest, Subsumes);
+
   void parse(const UChar* begin, const UChar* end);
 
+  // The algorothm is described more extensively here:
+  // https://w3c.github.io/webappsec-csp/embedded/#subsume-policy.
+  HashSet<String> getIntersect(const HashSet<String>& other);
+
   HashSet<String> m_pluginTypes;
 };