fix #607, add support for package config file

tool/global_compile.dart

 #!/usr/bin/env 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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/analyzer.dart'
     show
@@ skipping 10 matching lines @@
 
 void main(List<String> args) {
   // Parse flags.
   var parser = new ArgParser()
     ..addOption('out',
         help: 'Output file (defaults to "out.js")',
         abbr: 'o',
         defaultsTo: 'out.js')
     ..addFlag('unsafe-force-compile',
         help: 'Generate code with undefined behavior', negatable: false)
+    ..addOption('packages',
+        help:
+        'Path to the package resolution configuration file, which supplies '
+            'a mapping of package names to paths.  This option cannot be '
+            'used with --package-root.')
     ..addOption('package-root',
-        help: 'Directory containing packages',
         abbr: 'p',
-        defaultsTo: 'packages/')
+        help: 'Path to a package root directory (deprecated). This option '
+            'cannot be used with --packages.')
     ..addFlag('log', help: 'Show individual build commands')
     ..addOption('tmp',
         help:
             'Directory for temporary artifacts (defaults to a system tmp directory)');
 
   var options = parser.parse(args);
   if (options.rest.length != 1) {
     throw 'Expected a single dart entrypoint.';
   }
   var entry = options.rest.first;
   var outfile = options['out'] as String;
+  var packages = options['packages'] as String;
   var packageRoot = options['package-root'] as String;
   var unsafe = options['unsafe-force-compile'] as bool;
   var log = options['log'] as bool;
   var tmp = options['tmp'] as String;
 
   // Build an invocation to dartdevc
   var dartPath = Platform.resolvedExecutable;
   var ddcPath = path.dirname(path.dirname(Platform.script.toFilePath()));
   var template = [
     '$ddcPath/bin/dartdevc.dart',
     'compile',
     '--no-source-map', // Invalid as we're just concatenating files below
-    '-p',
-    packageRoot
   ];
+  if (packages != null) {
+    template.addAll(['--packages', packages]);
+  }
+  if (packageRoot != null) {
+    template.addAll(['--package-root', packageRoot]);
+  }
   if (unsafe) {
     template.add('--unsafe-force-compile');
   }
 
   // Compute the transitive closure
   var total = new Stopwatch()..start();
   var partial = new Stopwatch()..start();
 
   // TODO(vsm): We're using the analyzer just to compute the import/export/part
   // dependence graph.  This is expensive.  Is there a lighterweight way to do
@@ skipping 201 matching lines @@
         var uri = _resolveDirective(d);
         processDependence(entryPoint, canonicalize(uri, entryDir));
         transitiveFiles(uri, entryDir, packageRoot);
       } else if (d is PartDirective) {
         var uri = _resolveDirective(d);
         processFile(canonicalize(uri, entryDir));
       }
     }
   }
 }