Add Dart example.

examples/list_people.dart

diff --git a/examples/list_people.dart b/examples/list_people.dart
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+++ b/examples/list_people.dart
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+import 'dart:io';
+
+import 'dart_tutorial/addressbook.pb.dart';
+import 'dart_tutorial/addressbook.pbenum.dart';
+
+// Iterates though all people in the AddressBook and prints info about them.
+void printAddressBook(AddressBook addressBook) {
+  for (Person person in addressBook.people) {
+    print('Person ID: ${person.id}');
+    print('  Name: ${person.name}');
+    if (person.hasEmail()) {
+      print('  E-mail address:${person.email}');
+    }
+
+    for (Person_PhoneNumber phoneNumber in person.phones) {
+      switch (phoneNumber.type) {
+        case Person_PhoneType.MOBILE:
+          print('   Mobile phone #: ');
+          break;
+        case Person_PhoneType.HOME:
+          print('   Home phone #: ');
+          break;
+        case Person_PhoneType.WORK:
+          print('   Work phone #: ');
+          break;
+        default:
+          print('   Unknown phone #: ');
+          break;
+      }
+      print(phoneNumber.number);
+    }
+  }
+}
+
+// Reads the entire address book from a file and prints all
+// the information inside.
+main(List<String> arguments) {
+  if (arguments.length != 1) {
+    print('Usage: list_person ADDRESS_BOOK_FILE');
+    exit(-1);
+  }
+
+  // Read the existing address book.
+  File file = new File(arguments.first);
+  AddressBook addressBook = new AddressBook.fromBuffer(file.readAsBytesSync());
+  printAddressBook(addressBook);
+}