Prune shared extendion module after extension updating.

chrome/browser/extensions/shared_module_service.h

Index: chrome/browser/extensions/shared_module_service.h
diff --git a/chrome/browser/extensions/shared_module_service.h b/chrome/browser/extensions/shared_module_service.h
index d3462da91831c64126d655ba28f390d7fa6add1a..997273db4b3e43f244eda9cbcb2cbeec93101aa8 100644
--- a/chrome/browser/extensions/shared_module_service.h
+++ b/chrome/browser/extensions/shared_module_service.h
@@ -55,7 +55,13 @@ class SharedModuleService : public ExtensionRegistryObserver {
   scoped_ptr<ExtensionSet> GetDependentExtensions(const Extension* extension);
 
  private:
+  // Uninstall shared modules which are not used by other extensions.
+  void PruneSharedModules();
+
   // ExtensionRegistryObserver implementation.
+  virtual void OnExtensionInstalled(content::BrowserContext* browser_context,
+                                    const Extension* extension,
+                                    bool is_update) OVERRIDE;
   virtual void OnExtensionUninstalled(content::BrowserContext* browser_context,
                                       const Extension* extension) OVERRIDE;