Add seperate flag for download counts chart

Author: szakarias

app/lib/frontend/handlers/experimental.dart

@@ -96,6 +96,7 @@ class ExperimentalFlags {
   bool get isDarkModeDefault => isEnabled('dark-as-default');
 
   bool get showDownloadCounts => isEnabled('download-counts');
+  bool get showDownloadCountsChart => isEnabled('download-counts-chart');
 
   String encodedAsCookie() => _enabled.join(':');
 

app/lib/frontend/templates/views/pkg/score_tab.dart

@@ -80,7 +80,7 @@ d.Node scoreTabNode({
         ),
         _reportNode(report),
         if (card.weeklyVersionDownloads != null &&
-            requestContext.experimentalFlags.showDownloadCounts)
+            requestContext.experimentalFlags.showDownloadCountsChart)
           _downloadsChart(card.weeklyVersionDownloads!),
         if (toolEnvInfo != null) toolEnvInfo,
       ]),