Part 4.1: Is policy list subsumed under subsuming policy?

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

Index: third_party/WebKit/Source/core/frame/csp/ContentSecurityPolicy.h
diff --git a/third_party/WebKit/Source/core/frame/csp/ContentSecurityPolicy.h b/third_party/WebKit/Source/core/frame/csp/ContentSecurityPolicy.h
index 33368113da416347f23134e2a616dad8047b544b..128d5e9a8b87b653eb1a45f3203595dd379b17f5 100644
--- a/third_party/WebKit/Source/core/frame/csp/ContentSecurityPolicy.h
+++ b/third_party/WebKit/Source/core/frame/csp/ContentSecurityPolicy.h
@@ -356,6 +356,12 @@ class CORE_EXPORT ContentSecurityPolicy
   static const char* getDirectiveName(const DirectiveType&);
   static DirectiveType getDirectiveType(const String& name);
 
+  // This method checks if if this policy subsumes a given policy.
+  // Note the correct result is guaranteed if this policy contains only one
+  // CSPDirectiveList. More information here:
+  // https://w3c.github.io/webappsec-csp/embedded/#subsume-policy
+  bool subsumes(const ContentSecurityPolicy&);
+
   Document* document() const;
 
  private: