Compute all canonical names only for libraries being serialized.

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 c6653299d58d6ea1695e71f29c5db6bf45f7d9c4..d75a0fc7d25e13d750e189cd41b3b71caadb7d22 100644
--- a/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_kernel_generator_impl.dart
@@ -229,7 +229,6 @@ class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
           .toList();
 
       _logger.run('Serialize ${kernelLibraries.length} libraries', () {
-        program.unbindCanonicalNames();
         program.uriToSource.clear();
         List<int> bytes = _writeProgramBytes(program, kernelLibraries.contains);
         _byteStore.put(kernelKey, bytes);