Introduce HostID and de-couple Extensions from "script injection System" [browser side]

extensions/common/consumer.h

Index: extensions/common/consumer.h
diff --git a/extensions/common/consumer.h b/extensions/common/consumer.h
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+++ b/extensions/common/consumer.h
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+// Copyright 2014 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 EXTENSIONS_COMMON_CONSUMER_H_
+#define EXTENSIONS_COMMON_CONSUMER_H_
+
+#include <string>
+
+#include "base/macros.h"
+
+// IDs of API consumers who own user scripts.
+// For example: an extension, a <webview> created by an extension,
+// a <webview> created by WebUI, ...
+class ConsumerID {
+ public:
+  // The type of a host who contains regular tabs or <webview>s.
+  enum HostType { EXTENSIONS, WEBUI };
+
+  enum InstanceType { TAB, WEBVIEW };
+
+  // Default instance ID of a consumer who owns staticlly-defined user scripts.
+  static const int kDefaultInstanceID;
+
+  ConsumerID();
+  explicit ConsumerID(const ConsumerID& other);
+  ConsumerID(HostType host_type,
+             const std::string& host_id,
+             InstanceType instance_type,
+             int instance_id);
+  ~ConsumerID();
+
+  bool operator<(const ConsumerID& id) const;
+
+  HostType host_type() const { return host_type_; }
+  const std::string& host_id() const { return host_id_; }
+  InstanceType instance_type() const { return instance_type_; }
+  int instance_id() const { return instance_id_; }
+
+ private:
+  // Extension, or WebUI, ...
+  const HostType host_type_;
+
+  // Similar to extension_id, host_id is a uniquely indentifier for a host,
+  // e.g., an Extension or WebUI.
+  const std::string host_id_;
+
+  // A tab or a <webiew>.
+  const InstanceType instance_type_;
+
+  // For a consumer that owns staticlly defined user scripts, the
+  // |instance_id| is 0;
+  // For a consumer that owns declarative user scripts, the |instance_id|
+  // is assigned by DeclarativeUserScriptManager when the consumer requests a
+  // master object.
+  const int instance_id_;
+};
+
+// Represents an API consumer.
+class Consumer {
+ public:
+  Consumer();
+  virtual ~Consumer();
+
+  DISALLOW_COPY_AND_ASSIGN(Consumer);
+};
+
+#endif  // EXTENSIONS_COMMON_CONSUMER_H_