Implement and test CanonicalCookie::IsCanonical()

net/cookies/parsed_cookie.h

Index: net/cookies/parsed_cookie.h
diff --git a/net/cookies/parsed_cookie.h b/net/cookies/parsed_cookie.h
index 5e6f615e2aa096330253a302a11542f67eb97306..8bc5e99b67896ffe2e67ea30315dda9ac2c84c2e 100644
--- a/net/cookies/parsed_cookie.h
+++ b/net/cookies/parsed_cookie.h
@@ -103,6 +103,9 @@ class NET_EXPORT ParsedCookie {
   static std::string ParseTokenString(const std::string& token);
   static std::string ParseValueString(const std::string& value);
 
+  // Is the string valid as the value of a cookie attribute?
+  static bool IsValidCookieAttributeValue(const std::string& value);
+
  private:
   void ParseTokenValuePairs(const std::string& cookie_line);
   void SetupAttributes();