Drop the crypto dependency.

lib/src/runner/browser/platform.dart

Index: lib/src/runner/browser/platform.dart
diff --git a/lib/src/runner/browser/platform.dart b/lib/src/runner/browser/platform.dart
index 9603212a1f428a05682e1d6c84846e539ca257f7..f1a4b2999f795a463911c995d1c47df7f295cf73 100644
--- a/lib/src/runner/browser/platform.dart
+++ b/lib/src/runner/browser/platform.dart
@@ -49,7 +49,7 @@ class BrowserPlatform extends PlatformPlugin {
   ///
   /// This is used to ensure that other users on the same system can't snoop
   /// on data being served through this server.
-  final _secret = randomBase64(24, urlSafe: true);
+  final _secret = Uri.encodeComponent(randomBase64(24));
 
   /// The URL for this server.
   Uri get url => _server.url.resolve(_secret + "/");