src/vs/workbench/contrib/extensions/browser/extensionsWorkbenchService.ts/Extensions/onInstallExtension
class Extensions:	private onInstallExtension(event: InstallExtensionEvent): void {
		const { source } = event;
		if (source && !URI.isUri(source)) {
			const extension = this.installed.filter(e => areSameExtensions(e.identifier, source.identifier))[0]
				|| this.instantiationService.createInstance(Extension, this.stateProvider, this.server, undefined, source);
			this.installing.push(extension);
			this._onChange.fire({ extension });
		}
	}