Stream server logs to browser

Summary: Makes Flipper Logs tab functional for Flipper Browser

Reviewed By: lblasa

Differential Revision: D37459924

fbshipit-source-id: 4ebf3d47fbbf90bb367e01986b12dec782b03c34

desktop/flipper-server/src/logger.tsx

@@ -88,8 +88,15 @@ export function initializeLogger(staticDir: string) {
   const logger = createLogger();
   setLoggerInstance(logger);
 
+  let onConsoleEntry: ((entry: LoggerInfo) => void) | undefined;
+
   const file = fs.createWriteStream(path.join(staticDir, loggerOutputFile));
   consoleProxy((entry: LoggerInfo) => {
     file.write(`${JSON.stringify(entry)}\n`);
+    onConsoleEntry?.(entry);
   });
+
+  return (newOnConsoleEntry: (entry: LoggerInfo) => void) => {
+    onConsoleEntry = newOnConsoleEntry;
+  };
 }