fix checked-mode failure in perf_test

pkg/compiler/tool/perf.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// An entrypoint used to run portions of dart2js and measure its performance.
 library compiler.tool.perf;
 
 import 'dart:async';
 import 'dart:io';
 
@@ skipping 349 matching lines @@
             supportSerialization: serialization.supportSerialization);
 
         phase = Compiler.PHASE_RESOLVING;
         resolutionEnqueuer.applyImpact(mainImpact);
         // Note: we enqueue everything in the program so we measure generating
         // kernel for the entire code, not just what's reachable from main.
         libraryLoader.libraries.forEach((LibraryEntity library) {
           resolutionEnqueuer.applyImpact(computeImpactForLibrary(library));
         });
 
-        resolveLibraryMetadata();
+        if (commonElements.mirrorsLibrary != null) {
+          resolveLibraryMetadata();
+        }
         reporter.log('Resolving...');
         processQueue(resolutionEnqueuer, mainFunction, libraryLoader.libraries);
         resolutionEnqueuer.logSummary(reporter.log);
 
         (reporter as CompilerDiagnosticReporter)
             .reportSuppressedMessagesSummary();
 
         if (compilationFailed) {
           // TODO(sigmund): more diagnostics?
           print('compilation failed!');
           exit(1);
         }
 
         backend.onResolutionEnd();
         closeResolution();
         var program = (backend as dynamic).kernelTask.program;
         print('total libraries: ${program.libraries.length}');
       });
 }