[testing_app] Migrate to null safety (#800)

testing_app/pubspec.lock

@@ -105,7 +105,7 @@ packages:
       name: cupertino_icons
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.0"
+    version: "1.0.3"
   fake_async:
     dependency: transitive
     description:
@@ -163,11 +163,9 @@ packages:
     version: "4.0.0"
   integration_test:
     dependency: "direct dev"
-    description:
-      name: integration_test
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.0.2+3"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   io:
     dependency: transitive
     description:
@@ -216,7 +214,7 @@ packages:
       name: nested
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.0.4"
+    version: "1.0.0"
   node_preamble:
     dependency: transitive
     description:
@@ -272,7 +270,7 @@ packages:
       name: provider
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.3.3"
+    version: "5.0.0"
   pub_semver:
     dependency: transitive
     description:
@@ -286,7 +284,7 @@ packages:
       name: shelf
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.1"
+    version: "1.1.4"
   shelf_packages_handler:
     dependency: transitive
     description:
@@ -424,7 +422,7 @@ packages:
       name: web_socket_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   webdriver:
     dependency: transitive
     description: