use cdn for manifest too

src/vs/platform/extensionManagement/node/extensionGalleryService.ts

@@ -385,7 +385,7 @@ export class ExtensionGalleryService implements IExtensionGalleryService {
 
 		return this.getCommonHeaders()
 			.then(headers => assign(headers, { 'Accept-Encoding': 'gzip' }))
-			.then(headers => this.requestService.request({ url, headers }))
+			.then(headers => this._getAsset({ url, headers }))
 			.then(context => asJson<IExtensionManifest>(context))
 			.then(manifest => {
 				const desc = {