Install CRX updates one at a time.

chrome/browser/extensions/extension_service.h

Index: chrome/browser/extensions/extension_service.h
diff --git a/chrome/browser/extensions/extension_service.h b/chrome/browser/extensions/extension_service.h
index 1771e4e9dcfd51cef830a4b2c8f92825c684b969..28a6db1943ab9a30feb3ef297c1c420954e20ca2 100644
--- a/chrome/browser/extensions/extension_service.h
+++ b/chrome/browser/extensions/extension_service.h
@@ -36,6 +36,7 @@
 #include "content/browser/browser_thread.h"
 #include "content/common/notification_observer.h"
 #include "content/common/notification_registrar.h"
+#include "content/common/notification_source.h"
 #include "content/common/property_bag.h"
 
 class CrxInstaller;
@@ -64,9 +65,11 @@ class ExtensionServiceInterface {
   virtual ~ExtensionServiceInterface() {}
   virtual const ExtensionList* extensions() const = 0;
   virtual PendingExtensionManager* pending_extension_manager() = 0;
-  virtual void UpdateExtension(const std::string& id,
-                               const FilePath& path,
-                               const GURL& download_url) = 0;
+  virtual bool UpdateExtension(
+      const std::string& id,
+      const FilePath& path,
+      const GURL& download_url,
+      Source<CrxInstaller>* out_install_notification_source) = 0;

[Matt Perry, 2011/05/31 21:34:25]

Why a Source? Let's just pass a raw pointer out.

[Sam Kerner (Chrome), 2011/05/31 23:16:15]

Done.

   virtual const Extension* GetExtensionById(const std::string& id,
                                             bool include_disabled) const = 0;
   virtual const Extension* GetInstalledExtension(
@@ -262,9 +265,11 @@ class ExtensionService
   // |extension_path|.
   // TODO(aa): This method can be removed. ExtensionUpdater could use
   // CrxInstaller directly instead.
-  virtual void UpdateExtension(const std::string& id,
-                               const FilePath& extension_path,
-                               const GURL& download_url) OVERRIDE;
+  virtual bool UpdateExtension(
+      const std::string& id,
+      const FilePath& extension_path,
+      const GURL& download_url,
+      Source<CrxInstaller>* out_install_notification_source) OVERRIDE;
 
   // Reloads the specified extension.
   void ReloadExtension(const std::string& extension_id);