First cut at the component observer.

chrome/browser/component_updater/component_updater_service.h

Index: chrome/browser/component_updater/component_updater_service.h
diff --git a/chrome/browser/component_updater/component_updater_service.h b/chrome/browser/component_updater/component_updater_service.h
index 7125ff417534eb13c79a26355f9e274abfa3a5fd..a2291df2d2f4e6c67c8f40c6588a1d15caa6125b 100644
--- a/chrome/browser/component_updater/component_updater_service.h
+++ b/chrome/browser/component_updater/component_updater_service.h
@@ -50,6 +50,32 @@ class ComponentInstaller {
   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
@@ -58,6 +84,7 @@ class ComponentInstaller {
 struct CrxComponent {
   std::vector<uint8> pk_hash;
   ComponentInstaller* installer;
+  ComponentObserver* observer;
   Version version;
   std::string fingerprint;
   std::string name;