Add a function triggering extension installed to ExtensionRegistryObserver

extensions/browser/extension_registry_observer.h

 // 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_BROWSER_EXTENSION_REGISTRY_OBSERVER_H_
 #define EXTENSIONS_BROWSER_EXTENSION_REGISTRY_OBSERVER_H_
 
 #include "extensions/common/extension.h"
 
 namespace content {
@@ skipping 15 matching lines @@
   // in the enabled_extensions set of ExtensionRegistry.
   virtual void OnExtensionLoaded(
       content::BrowserContext* browser_context,
       const Extension* extension) {}
 
   // Called after an extension is unloaded. The extension no longer exists in
   // any of the ExtensionRegistry sets (enabled, disabled, etc.).
   virtual void OnExtensionUnloaded(content::BrowserContext* browser_context,
                                    const Extension* extension,
                                    UnloadedExtensionInfo::Reason reason) {}
+
+  // Called an extension is about to finish install. The extension won't be in

[not at google - send to devlin, 2014/05/16 23:03:35]

Thanks for adding the comment. How about a slight variation:

Called when |extension| is about to be installed. |is_update| is true if the
installation is the result of it updating, in which case |old_name| is the name
of the extension's previous version.

The ExtensionRegistry will not be tracking |extension| at the time this event is
fired, but will be immediately afterwards (note: not necessarily enabled; it
might be installed in the disabled or even blacklisted sets, for example).

Note that it's much more common to care about extensions being loaded
(OnExtensionLoaded).

[limasdf, 2014/05/17 06:16:19]

Done. Thank you.

+  // ExtensionRegistry and about to appear in the ExtensionRegistry.
+  // (But could be in any of the sets(terminated, blacklisted, enabled ,.).
+  // Caller probably want to listen for |OnExtensionLoaded()| unless they really
+  // want to know when an extension is about to be installed.
+  virtual void OnExtensionWillBeInstalled(
+      content::BrowserContext* browser_context,
+      const Extension* extension,
+      bool is_update,
+      const std::string& old_name) {}
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_EXTENSION_REGISTRY_OBSERVER_H_