[dartdev] Update --enable-analytics to re-enable unified analytics

Previously, running `dart --disable-analytics` would disable this, but `dart --enable-analytics` would not re-enable.

Change-Id: I3da33f0c0ed9a3e29ff4fbbfd66ceeb030014c4b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/295522
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Janice Collins <jcollins@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/dartdev/lib/dartdev.dart

@@ -172,6 +172,11 @@ class DartdevRunner extends CommandRunner<int> {
     } else if (topLevelResults['enable-analytics']) {
       analytics.enabled = true;
 
+      // Enable sending data via the unified analytics package.
+      var unifiedAnalytics = createUnifiedAnalytics();
+      await unifiedAnalytics.setTelemetry(true);
+      unifiedAnalytics.close();
+
       // Alert the user again that data will be collected.
       print(analyticsNoticeOnFirstRunMessage);
       return 0;