Add version validation for LookupMap, also add unittest directly in LookupMap (take 2)

pkg/compiler/lib/src/compiler.dart

 // Copyright (c) 2012, 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.compiler_base;
 
 import 'dart:async' show
     EventSink,
     Future;
 
@@ skipping 1135 matching lines @@
 
     log('Inferring types...');
     typesTask.onResolutionComplete(mainFunction);
 
     if (stopAfterTypeInference) return;
 
     backend.onTypeInferenceComplete();
 
     log('Compiling...');
     phase = PHASE_COMPILING;
+    backend.onCodegenStart();
     // TODO(johnniwinther): Move these to [CodegenEnqueuer].
     if (hasIsolateSupport) {
       backend.enableIsolateSupport(enqueuer.codegen);
     }
     if (compileAll) {
       libraryLoader.libraries.forEach((LibraryElement library) {
         fullyEnqueueLibrary(library, enqueuer.codegen);
       });
     }
     processQueue(enqueuer.codegen, mainFunction);
@@ skipping 618 matching lines @@
 
   @override
   InterfaceType streamType([DartType elementType]) {
     InterfaceType type = streamClass.computeType(compiler);
     if (elementType == null) {
       return streamClass.rawType;
     }
     return type.createInstantiation([elementType]);
   }
 }