dart2js: Measure time of individual optimization passes.

tests/compiler/dart2js/memory_compiler.dart

 // Copyright (c) 2013, 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.
 
 library dart2js.test.memory_compiler;
 
 import 'dart:async';
 
 import 'package:compiler/compiler.dart' show
     DiagnosticHandler;
@@ skipping 245 matching lines @@
     // is a stale reference to an old compiler object.  By nulling out the old
     // compiler's fields, such stale references are easier to identify.
     cachedCompiler.scanner = null;
     cachedCompiler.dietParser = null;
     cachedCompiler.parser = null;
     cachedCompiler.patchParser = null;
     cachedCompiler.libraryLoader = null;
     cachedCompiler.resolver = null;
     cachedCompiler.closureToClassMapper = null;
     cachedCompiler.checker = null;
-    cachedCompiler.irBuilder = null;
     cachedCompiler.typesTask = null;
     cachedCompiler.backend = null;
     // Don't null out the enqueuer as it prevents us from using cachedCompiler
     // more than once.
     cachedCompiler.deferredLoadTask = null;
     cachedCompiler.mirrorUsageAnalyzerTask = null;
     cachedCompiler.dumpInfoTask = null;
     cachedCompiler.buildId = null;
   }
   return compiler;
@@ skipping 54 matching lines @@
       createDiagnosticHandler(diagnosticHandler, provider, showDiagnostics);
 
   List<Uri> libraries = <Uri>[];
   memorySourceFiles.forEach((String path, _) {
     libraries.add(new Uri(scheme: 'memory', path: path));
   });
 
   return analyze(libraries, libraryRoot, packageRoot,
                  provider, handler, options);
 }