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

chrome/browser/extensions/extension_user_script_loader.h

Index: chrome/browser/extensions/extension_user_script_loader.h
diff --git a/chrome/browser/extensions/extension_user_script_loader.h b/chrome/browser/extensions/extension_user_script_loader.h
new file mode 100644
index 0000000000000000000000000000000000000000..f23f57aed065c7e27a9aa413e1c8ca78895c784d
--- /dev/null
+++ b/chrome/browser/extensions/extension_user_script_loader.h
@@ -0,0 +1,59 @@
+// Copyright 2015 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_USER_SCRIPT_LOADER_H_
+#define CHROME_BROWSER_EXTENSIONS_EXTENSION_USER_SCRIPT_LOADER_H_
+
+#include "base/memory/shared_memory.h"
+#include "chrome/browser/extensions/user_script_loader.h"
+#include "extensions/browser/extension_registry_observer.h"
+#include "extensions/common/extension.h"
+
+namespace content {
+class BrowserContext;
+}
+
+class Profile;
+
+namespace extensions {
+
+class ExtensionRegistry;
+
+// UserScriptLoader for extensions.
+class ExtensionUserScriptLoader : public UserScriptLoader,
+                                  public ExtensionRegistryObserver {
+ public:
+  // The listen_for_extension_system_loaded is only set true when initilizing
+  // the Extension System, e.g, when constructs SharedUserScriptMaster in
+  // ExtensionSystemImpl.
+  ExtensionUserScriptLoader(Profile* profile,
+                            const HostID& host_id,
+                            bool listen_for_extension_system_loaded);
+  ~ExtensionUserScriptLoader() override;
+
+ private:
+  // UserScriptLoader:
+  void UpdateHostsInfo(const std::set<HostID>& changed_hosts) override;
+  LoadUserScriptsContentFunction GetLoadUserScriptsFunction() override;
+
+  // ExtensionRegistryObserver:
+  void OnExtensionUnloaded(content::BrowserContext* browser_context,
+                           const Extension* extension,
+                           UnloadedExtensionInfo::Reason reason) override;
+
+  // Initiates script load when we have been waiting for the extension system
+  // to be ready.
+  void OnExtensionSystemReady();
+
+  ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
+      extension_registry_observer_;
+
+  base::WeakPtrFactory<ExtensionUserScriptLoader> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExtensionUserScriptLoader);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_USER_SCRIPT_LOADER_H_