Use precomputed uriBytes while computing cycle signature.

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

Index: pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
diff --git a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
index 4b1ca3273197de89fd8042b5761aa4a4f8f9d674..daff92492b7f5bf6d67378210c91de80962cfde9 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -317,7 +317,7 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
 
     // Append API signatures of transitive files.
     for (var file in transitiveFiles) {
-      signatureBuilder.addString(file.uri.toString());
+      signatureBuilder.addBytes(file.uriBytes);
       // TODO(scheglov): Stop using content hashes here, when Kernel stops
       // copying methods of mixed-in classes.
       // https://github.com/dart-lang/sdk/issues/29881