Fix typo in lookup map, use pub_semver to check version constraints in dart2js

pkg/compiler/lib/src/js_backend/lookup_map_analysis.dart

 // Copyright (c) 2015, 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.
 
 /// Analysis to determine how to generate code for `LookupMap`s.
 library compiler.src.js_backend.lookup_map_analysis;
 
 import '../common/registry.dart' show Registry;
 import '../compiler.dart' show Compiler;
 import '../diagnostics/messages.dart' show MessageKind;
@@ skipping 10 matching lines @@
     Element,
     Elements,
     FieldElement,
     FunctionElement,
     FunctionSignature,
     LibraryElement,
     VariableElement;
 import '../enqueue.dart' show Enqueuer;
 import 'js_backend.dart' show JavaScriptBackend;
 import '../dart_types.dart' show DynamicType, InterfaceType;
+import 'package:pub_semver/pub_semver.dart';
 
 /// An analysis and optimization to remove unused entries from a `LookupMap`.
 ///
 /// `LookupMaps` are defined in `package:lookup_map/lookup_map.dart`. They are
 /// simple maps that contain constant expressions as keys, and that only support
 /// the lookup operation.
 ///
 /// This analysis and optimization will tree-shake the contents of the maps by
 /// looking at the program and finding which keys are clearly unused. Not all
 /// constants can be approximated statically, so this optimization is limited to
@@ skipping 114 matching lines @@
     StringConstantValue value =
         backend.constants.getConstantValueForVariable(lookupMapVersionVariable);
     if (value == null) {
       backend.compiler.reportInfo(lookupMapVersionVariable,
           MessageKind.UNRECOGNIZED_VERSION_OF_LOOKUP_MAP);
       return;
     }
 
     // TODO(sigmund): add proper version resolution using the pub_semver package
     // when we introduce the next version.
-    String version = value.primitiveValue.slowToString();
-    if (version != '0.0.1') {
+    Version version;
+    try {
+      version = new Version.parse(value.primitiveValue.slowToString());
+    } catch (e) {}
+
+    if (version == null || !_validLookupMapVersionConstraint.allows(version)) {
       backend.compiler.reportInfo(lookupMapVersionVariable,
           MessageKind.UNRECOGNIZED_VERSION_OF_LOOKUP_MAP);
       return;
     }
 
     ClassElement cls = lookupMapLibrary.findLocal('LookupMap');
     cls.computeType(backend.compiler);
     entriesField = cls.lookupMember('_entries');
     keyField = cls.lookupMember('_key');
     valueField = cls.lookupMember('_value');
@@ skipping 246 matching lines @@
       if (keyValuePairs.length == 2) {
         original.fields[analysis.keyField] = keyValuePairs[0];
         original.fields[analysis.valueField] = keyValuePairs[1];
       }
     } else {
       original.fields[analysis.entriesField] =
           new ListConstantValue(listType, keyValuePairs);
     }
   }
 }
+
+final _validLookupMapVersionConstraint =
+    new VersionConstraint.parse('^0.0.1');