Fix all the analysis hints in pub.

sdk/lib/_internal/pub/lib/src/command/serve.dart

Index: sdk/lib/_internal/pub/lib/src/command/serve.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/serve.dart b/sdk/lib/_internal/pub/lib/src/command/serve.dart
index 32074fc90fbd20bb3479b8148d5a21c5cd091b42..d7e9de5f56f7724bc9cbedec5b36de47d0fa7bbb 100644
--- a/sdk/lib/_internal/pub/lib/src/command/serve.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/serve.dart
@@ -10,7 +10,6 @@ import 'dart:math' as math;
 import 'package:barback/barback.dart';
 
 import '../barback/asset_environment.dart';
-import '../barback/pub_package_provider.dart';
 import '../log.dart' as log;
 import '../utils.dart';
 import 'barback.dart';
@@ -27,8 +26,6 @@ class ServeCommand extends BarbackCommand {
   String get invocation => "pub serve [directories...]";
   String get docUrl => "http://dartlang.org/tools/pub/cmd/pub-serve.html";
 
-  PubPackageProvider _provider;
-
   String get hostname => argResults['hostname'];
 
   /// The base port for the servers.
@@ -59,6 +56,9 @@ class ServeCommand extends BarbackCommand {
   final _completer = new Completer();
 
   ServeCommand() {
+    argParser.addOption("define", abbr: "D",
+        help: "Defines an environment constant for dart2js.",
+        allowMultiple: true, splitCommas: false);
     argParser.addOption('hostname', defaultsTo: 'localhost',
         help: 'The hostname to listen on.');
     argParser.addOption('port', defaultsTo: '8080',
@@ -88,9 +88,13 @@ class ServeCommand extends BarbackCommand {
     var watcherType = argResults['force-poll'] ?
         WatcherType.POLLING : WatcherType.AUTO;
 
+    var environmentConstants = new Map.fromIterable(argResults["define"],
+        key: (pair) => pair.split("=").first,
+        value: (pair) => pair.split("=").last);
+
     var environment = await AssetEnvironment.create(entrypoint, mode,
         watcherType: watcherType, hostname: hostname, basePort: port,
-        useDart2JS: useDart2JS);
+        useDart2JS: useDart2JS, environmentConstants: environmentConstants);
     var directoryLength = sourceDirectories.map((dir) => dir.length)
         .reduce(math.max);