src/vs/workbench/api/browser/mainThreadWebviews.ts/MainThreadWebviews/$postMessage
class MainThreadWebviews:	public async $postMessage(handle: extHostProtocol.WebviewHandle, jsonMessage: string, ...buffers: VSBuffer[]): Promise<boolean> {
		const webview = this.getWebview(handle);
		const { message, arrayBuffers } = deserializeWebviewMessage(jsonMessage, buffers);
		return webview.postMessage(message, arrayBuffers);
	}