Fix gsutil argument order. (#14808)

dev/bots/prepare_package.dart

@@ -487,14 +487,13 @@ class ArchivePublisher {
     if (dest.endsWith('.json')) {
       mimeType = 'application/json';
     }
-    final List<String> args = <String>['cp'];
+    final List<String> args = <String>[];
     // Use our preferred MIME type for the files we care about
     // and let gsutil figure it out for anything else.
     if (mimeType != null) {
       args.addAll(<String>['-h', 'Content-Type:$mimeType']);
     }
-    args.add(src);
-    args.add(dest);
+    args.addAll(<String>['cp', src, dest]);
     return _runGsUtil(args);
   }
 }

dev/bots/test/prepare_package_test.dart

@@ -239,10 +239,10 @@ void main() {
 ''';
         final Map<String, List<ProcessResult>> calls = <String, List<ProcessResult>>{
           'gsutil rm $gsArchivePath': null,
-          'gsutil cp -h Content-Type:$archiveMime $archivePath $gsArchivePath': null,
+          'gsutil -h Content-Type:$archiveMime cp $archivePath $gsArchivePath': null,
           'gsutil cat $gsJsonPath': <ProcessResult>[new ProcessResult(0, 0, releasesJson, '')],
           'gsutil rm $gsJsonPath': null,
-          'gsutil cp -h Content-Type:application/json $jsonPath $gsJsonPath': null,
+          'gsutil -h Content-Type:application/json cp $jsonPath $gsJsonPath': null,
         };
         processManager.fakeResults = calls;
         final File outputFile = new File(path.join(tempDir.absolute.path, archiveName));