Don’t pod unless there are plugins (#9701)

packages/flutter_tools/lib/src/ios/mac.dart

@@ -152,9 +152,10 @@ Future<XcodeBuildResult> buildXcodeProject({
   // copied over to a location that is suitable for Xcodebuild to find them.
   final Directory appDirectory = fs.directory(app.appDirectory);
   await _addServicesToBundle(appDirectory);
-  injectPlugins();
+  final bool hasFlutterPlugins = injectPlugins();
 
-  await _runPodInstall(appDirectory, flutterFrameworkDir(mode));
+  if (hasFlutterPlugins)
+    await _runPodInstall(appDirectory, flutterFrameworkDir(mode));
 
   final List<String> commands = <String>[
     '/usr/bin/env',

packages/flutter_tools/lib/src/plugins.dart

@@ -194,7 +194,11 @@ void _writeIOSPluginRegistry(String directory, List<Plugin> plugins) {
 
 }
 
-void injectPlugins({String directory}) {
+/// Finds Flutter plugins in the pubspec.yaml, creates platform injection
+/// registries classes and add them to the build depedencies.
+///
+/// Returns whether any Flutter plugins are added.
+bool injectPlugins({String directory}) {
   directory ??= fs.currentDirectory.path;
   final List<Plugin> plugins = _findPlugins(directory);
   _writeFlutterPluginsList(directory, plugins);
@@ -202,4 +206,5 @@ void injectPlugins({String directory}) {
     _writeAndroidPluginRegistry(directory, plugins);
   if (fs.isDirectorySync(fs.path.join(directory, 'ios')))
     _writeIOSPluginRegistry(directory, plugins);
+  return plugins.isNotEmpty;
 }