Mark analyzer_cli as strong-mode clean

pkg/analyzer_cli/lib/src/build_mode.dart

Index: pkg/analyzer_cli/lib/src/build_mode.dart
diff --git a/pkg/analyzer_cli/lib/src/build_mode.dart b/pkg/analyzer_cli/lib/src/build_mode.dart
index f79e4012f324a6699eb51b73a3a6af328f237e6f..18833187163ba273a1276434682b0a2995224027 100644
--- a/pkg/analyzer_cli/lib/src/build_mode.dart
+++ b/pkg/analyzer_cli/lib/src/build_mode.dart
@@ -69,7 +69,7 @@ class AnalyzerWorkerLoop extends SyncWorkerLoop {
     try {
       // Add in the dart-sdk argument if `dartSdkPath` is not null, otherwise it
       // will try to find the currently installed sdk.
-      var arguments = new List.from(request.arguments);
+      var arguments = new List<String>.from(request.arguments);
       if (dartSdkPath != null &&
           !arguments.any((arg) => arg.startsWith('--dart-sdk'))) {
         arguments.add('--dart-sdk=$dartSdkPath');