Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/analyzer/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();
+  }
+}