Observe adding external extensions via windows registry.

chrome/browser/extensions/external_provider_impl.cc

Index: chrome/browser/extensions/external_provider_impl.cc
diff --git a/chrome/browser/extensions/external_provider_impl.cc b/chrome/browser/extensions/external_provider_impl.cc
index 9b62f0f43c3d092d0295db9f60867bb8f8e6b31c..8c31e2a2ba8ab3e2cd958ddc09839eb1cb9178da 100644
--- a/chrome/browser/extensions/external_provider_impl.cc
+++ b/chrome/browser/extensions/external_provider_impl.cc
@@ -119,7 +119,44 @@ void ExternalProviderImpl::SetPrefs(base::DictionaryValue* prefs) {
 
   prefs_.reset(prefs);
   ready_ = true;  // Queries for extensions are allowed from this point.
+  NotifyExtensionsFromPrefs(true);
+  service_->OnExternalProviderReady(this);
+}
+
+void ExternalProviderImpl::UpdatePrefs(base::DictionaryValue* prefs) {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  // We only expect updates from windows registry.
+  CHECK(crx_location_ == Manifest::EXTERNAL_REGISTRY);
+
+  // Check if the service is still alive. It is possible that it went
+  // away while |loader_| was working on the FILE thread.
+  if (!service_)
+    return;
 
+  std::set<std::string> removed_extensions;
+  // Find extensions that were removed by this ExternalProvider.
+  for (base::DictionaryValue::Iterator i(*prefs_); !i.IsAtEnd(); i.Advance()) {
+    const std::string& extension_id = i.key();
+    // Don't bother about invalid ids.
+    if (!crx_file::id_util::IdIsValid(extension_id))
+      continue;
+    if (!prefs->HasKey(extension_id))
+      removed_extensions.insert(extension_id);
+  }
+
+  prefs_.reset(prefs);
+
+  // Notify ExtensionService about all the extension this provider has found
+  // "updates" for.
+  // For each update found, this will end up calling
+  // OnExternalExtensionUpdateUrlFound() or OnExternalExtensionFileFound().
+  NotifyExtensionsFromPrefs(false);
+  // Then notify about the completion of update, with list of extensions that
+  // were removed.
+  service_->OnExternalProviderUpdateComplete(this, removed_extensions);
+}
+
+void ExternalProviderImpl::NotifyExtensionsFromPrefs(bool is_initial_load) {
   // Set of unsupported extensions that need to be deleted from prefs_.
   std::set<std::string> unsupported_extensions;
 
@@ -320,7 +357,8 @@ void ExternalProviderImpl::SetPrefs(base::DictionaryValue* prefs) {
                                                   update_url,
                                                   download_location_,
                                                   creation_flags,
-                                                  auto_acknowledge_);
+                                                  auto_acknowledge_,
+                                                  is_initial_load);
     }
   }
 
@@ -330,8 +368,6 @@ void ExternalProviderImpl::SetPrefs(base::DictionaryValue* prefs) {
     // will be uninstalled later because provider doesn't provide it anymore.
     prefs_->Remove(*it, NULL);
   }
-
-  service_->OnExternalProviderReady(this);
 }
 
 void ExternalProviderImpl::ServiceShutdown() {