src/vs/workbench/contrib/webview/browser/webviewElement.ts/WebviewElement/_send
class WebviewElement:	private async _send<K extends keyof ToWebviewMessage>(channel: K, data: ToWebviewMessage[K], _createElement: Transferable[] = []): Promise<boolean> {
		if (this._state.type === WebviewState.Type.Initializing) {
			let resolve: (x: boolean) => void;
			const promise = new Promise<boolean>(r => resolve = r);
			this._state.pendingMessages.push({ channel, data, transferable: _createElement, resolve: resolve! });
			return promise;
		} else {
			return this.doPostMessage(channel, data, _createElement);
		}
	}