src/vs/workbench/contrib/webview/browser/webviewElement.ts/WebviewElement/doPostMessage
class WebviewElement:	private doPostMessage(channel: string, data?: any, transferable: Transferable[] = []): boolean {
		if (this.element && this._messagePort) {
			this._messagePort.postMessage({ channel, args: data }, transferable);
			return true;
		}
		return false;
	}