First cut at the component observer.

chrome/browser/component_updater/component_updater_service.h

 // Copyright (c) 2012 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_COMPONENT_UPDATER_COMPONENT_UPDATER_SERVICE_H_
 #define CHROME_BROWSER_COMPONENT_UPDATER_COMPONENT_UPDATER_SERVICE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 32 matching lines @@
   // the filename of the file in this component's CRX. Returns false if this is
   // not possible (the file has been removed or modified, or its current
   // location is unknown). Otherwise, returns true.
   virtual bool GetInstalledFile(const std::string& file,
                                 base::FilePath* installed_file) = 0;
 
  protected:
   virtual ~ComponentInstaller() {}
 };
 
+// Defines an interface to observe a CrxComponent.
+class ComponentObserver {
+ public:
+  enum Events {
+    // Sent when the component updater starts doing update checks.
+    COMPONENT_UPDATER_STARTED,
+
+    // Sent when the component updater is going to take a long nap.
+    COMPONENT_UPDATER_SLEEPING,
+
+    // Sent when there is a new version of a registered component. After
+    // the notification is sent the component will be downloaded.
+    COMPONENT_UPDATE_FOUND,
+
+    // Sent when the new component has been downloaded and an installation
+    // or upgrade is about to be attempted.
+    COMPONENT_UPDATE_READY,
+  };
+
+  virtual ~ComponentObserver() {}
+
+  // The component updater service will call this function when an interesting
+  // event happens for a specific component. |extra| is |event| dependent.
+  virtual void OnEvent(Events event, int extra) = 0;
+};
+
 // Describes a particular component that can be installed or updated. This
 // structure is required to register a component with the component updater.
 // |pk_hash| is the SHA256 hash of the component's public key. If the component
 // is to be installed then version should be "0" or "0.0", else it should be
 // the current version. |fingerprint| and |name| are optional.

[cpu_(ooo_6.6-7.5), 2013/07/31 21:59:36]

mention that observer is also optional.

[Sorin Jianu, 2013/07/31 22:29:48]

Done.

 struct CrxComponent {
   std::vector<uint8> pk_hash;
   ComponentInstaller* installer;
+  ComponentObserver* observer;
   Version version;
   std::string fingerprint;
   std::string name;
   CrxComponent();
   ~CrxComponent();
 };
 
 // The component update service is in charge of installing or upgrading
 // select parts of chrome. Each part is called a component and managed by
 // instances of CrxComponent registered using RegisterComponent(). On the
@@ skipping 77 matching lines @@
 
   virtual ~ComponentUpdateService() {}
 };
 
 // Creates the component updater. You must pass a valid |config| allocated on
 // the heap which the component updater will own.
 ComponentUpdateService* ComponentUpdateServiceFactory(
     ComponentUpdateService::Configurator* config);
 
 #endif  // CHROME_BROWSER_COMPONENT_UPDATER_COMPONENT_UPDATER_SERVICE_H_