Roll Observatory packages and add a roll script

packages/analyzer/lib/src/generated/java_engine_io.dart

 library java.engine.io;
 
 import "dart:io";
 import "java_io.dart";
 
 class OSUtilities {
   static String LINE_SEPARATOR = isWindows() ? '\r\n' : '\n';
   static bool isWindows() => Platform.operatingSystem == 'windows';
   static bool isMac() => Platform.operatingSystem == 'macos';
 }
 
 class FileUtilities2 {
   static JavaFile createFile(String path) {
     return new JavaFile(path).getAbsoluteFile();
   }
 }