Consistently use namespaced base::Version in extensions code.

chrome/browser/extensions/webstore_installer.h

Index: chrome/browser/extensions/webstore_installer.h
diff --git a/chrome/browser/extensions/webstore_installer.h b/chrome/browser/extensions/webstore_installer.h
index f4736233a65e93b7c345b77e5e87f7faf0837ff4..473666ac582a55b6c4642a4293dcfc15044464de 100644
--- a/chrome/browser/extensions/webstore_installer.h
+++ b/chrome/browser/extensions/webstore_installer.h
@@ -156,7 +156,7 @@ class WebstoreInstaller : public content::NotificationObserver,
     scoped_refptr<Extension> dummy_extension;
 
     // Required minimum version.
-    std::unique_ptr<Version> minimum_version;
+    std::unique_ptr<base::Version> minimum_version;
 
     // The authuser index required to download the item being installed. May be
     // the empty string, in which case no authuser parameter is used.