Cache is_third_party requests in a one-entry cache.

components/subresource_filter/core/common/first_party_origin.h

Index: components/subresource_filter/core/common/first_party_origin.h
diff --git a/components/subresource_filter/core/common/first_party_origin.h b/components/subresource_filter/core/common/first_party_origin.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_SUBRESOURCE_FILTER_CORE_COMMON_FIRST_PARTY_ORIGIN_H_
+#define COMPONENTS_SUBRESOURCE_FILTER_CORE_COMMON_FIRST_PARTY_ORIGIN_H_
+
+#include <string>
+
+#include "url/gurl.h"
+#include "url/origin.h"
+
+namespace subresource_filter {
+
+// Encapsulates the first-party origin of a document, and provides fast (cached)
+// third-partiness checks against that origin, i.e. whether a given URL is
+// third-party in relation to the document's origin.
+//
+// It uses a simple one-entry cache to optimize for the case when a significant
+// number of consecutive URLs have the same domain.
+class FirstPartyOrigin {
+ public:
+  explicit FirstPartyOrigin(url::Origin document_origin);
+
+  const url::Origin& origin() const { return document_origin_; }
+
+  // Returns whether |url| is a third-party in relation to |this| origin. May
+  // return a cached value. May update the cache.
+  bool IsThirdParty(const GURL& url) const;
+
+  // Returns whether |url| is a third party in respect to |first_party_origin|.
+  static bool IsThirdParty(const GURL& url,
+                           const url::Origin& first_party_origin);
+
+ private:
+  url::Origin document_origin_;
+
+  // NOTE: GURL is needed to work around the slightly inefficient interfaces of
+  // net::registry_controlled_domains.
+  GURL document_origin_as_gurl_;
+
+  // One-entry cache that stores input/output of the last IsThirdParty
+  // call.
+  //
+  // NOTE: registry_controlled_domains::SameDomainOrHost takes GURLs as inputs,
+  // but the cache entry stores only the host part of a GURL. It is assumed that
+  // SameDomainOrHost will return the same result for a GURL which has the same
+  // non-empty host part as the cached one.
+  mutable std::string last_checked_host_;
+  mutable bool last_checked_host_was_third_party_ = false;
+};
+
+}  // namespace subresource_filter
+
+#endif  // COMPONENTS_SUBRESOURCE_FILTER_CORE_COMMON_FIRST_PARTY_ORIGIN_H_