src/vs/workbench/api/common/extHostWebview.ts/ExtHostWebviews/$onMessage
class ExtHostWebviews:	public $onMessage(
		handle: extHostProtocol.WebviewHandle,
		jsonMessage: string,
		buffers: SerializableObjectWithBuffers<VSBuffer[]>
	): void {
		const webview = this.getWebview(handle);
		if (webview) {
			const { message } = deserializeWebviewMessage(jsonMessage, buffers.value);
			webview._onMessageEmitter.fire(message);
		}
	}