add macos option

macos/Podfile

@@ -0,0 +1,58 @@
+platform :osx, '10.14'
+
+# CocoaPods analytics sends network stats synchronously affecting flutter build latency.
+ENV['COCOAPODS_DISABLE_STATS'] = 'true'
+
+project 'Runner', {
+  'Debug' => :debug,
+  'Profile' => :release,
+  'Release' => :release,
+}
+
+def flutter_root
+  generated_xcode_build_settings_path = File.expand_path(File.join('..', 'Flutter', 'ephemeral', 'Flutter-Generated.xcconfig'), __FILE__)
+  unless File.exist?(generated_xcode_build_settings_path)
+    raise "#{generated_xcode_build_settings_path} must exist. If you're running pod install manually, make sure \"flutter pub get\" is executed first"
+  end
+
+  File.foreach(generated_xcode_build_settings_path) do |line|
+    matches = line.match(/FLUTTER_ROOT\=(.*)/)
+    return matches[1].strip if matches
+  end
+  raise "FLUTTER_ROOT not found in #{generated_xcode_build_settings_path}. Try deleting Flutter-Generated.xcconfig, then run \"flutter pub get\""
+end
+
+require File.expand_path(File.join('packages', 'flutter_tools', 'bin', 'podhelper'), flutter_root)
+
+flutter_macos_podfile_setup
+
+target 'Runner' do
+  use_frameworks!
+  use_modular_headers!
+
+  flutter_install_all_macos_pods File.dirname(File.realpath(__FILE__))
+  target 'RunnerTests' do
+    inherit! :search_paths
+  end
+end
+
+post_install do |installer|
+  # Ensure pods also use the minimum deployment target set above
+  # https://stackoverflow.com/a/64385584/436422
+  puts 'Determining pod project minimum deployment target'
+
+  pods_project = installer.pods_project
+  deployment_target_key = 'MACOSX_DEPLOYMENT_TARGET'
+  deployment_targets = pods_project.build_configurations.map{ |config| config.build_settings[deployment_target_key] }
+  minimum_deployment_target = deployment_targets.min_by{ |version| Gem::Version.new(version) }
+
+  puts 'Minimal deployment target is ' + minimum_deployment_target
+  puts 'Setting each pod deployment target to ' + minimum_deployment_target
+
+  installer.pods_project.targets.each do |target|
+    flutter_additional_macos_build_settings(target)
+    target.build_configurations.each do |config|
+      config.build_settings[deployment_target_key] = minimum_deployment_target
+    end
+  end
+end