fix #607, add support for package config file

tool/global_compile.dart

Index: tool/global_compile.dart
diff --git a/tool/global_compile.dart b/tool/global_compile.dart
index 673660a1671cb9a7b4ff66c826b6f8454577a39d..ebe504f54c4077ff9264fa67cafbda7e8fc23f8d 100644
--- a/tool/global_compile.dart
+++ b/tool/global_compile.dart
@@ -28,10 +28,15 @@ void main(List<String> args) {
         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:
@@ -43,6 +48,7 @@ void main(List<String> args) {
   }
   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;
@@ -55,9 +61,13 @@ void main(List<String> args) {
     '$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');
   }