added package_root flag to standalone dart vm

runtime/bin/builtin.dart

Index: runtime/bin/builtin.dart
diff --git a/runtime/bin/builtin.dart b/runtime/bin/builtin.dart
index e0108096f6c8934346edbf6b103b0ea3dfe26d75..380842c6de2d139c823cd4fc071f9f7cca164ae1 100644
--- a/runtime/bin/builtin.dart
+++ b/runtime/bin/builtin.dart
@@ -32,6 +32,9 @@ var _is_windows;
 // package imports can be resolved relative to it.
 Uri _entrypoint;
 
+// The directory to look in to resolve "package:" scheme URIs.
+String _packageRoot;
+
 void _logResolution(String msg) {
   final enabled = false;
   if (enabled) {
@@ -39,6 +42,13 @@ void _logResolution(String msg) {
   }
 }
 
+String _setPackageRoot(String packageRoot) {
+  if (!packageRoot.endsWith("/")) {
+    packageRoot += "/";
+  }
+  _packageRoot = packageRoot;

[siva, 2012/04/22 00:14:01]

will windows users specify --package_root="c:\Users\billg\" or
--package_root="c:/Users/billg/" ?

The later one is not natural and if it is the former than the code you have in
builtin.dart for setting the package root may not work.


Also what happens if they specify "--package_root=c:" meaning current directory
in drive c: ?

[mattsh, 2012/04/23 16:48:09]

Adding a TODO to decide about forward slashes and drive letters.

[siva, 2012/04/23 17:16:45]

We would like to not postpone windows issues for a later date as we seem to have
numerous windows users lately who have been complaining if things don't work.

On 2012/04/23 16:48:09, mattsh wrote:

+}
+
 String _resolveScriptUri(String cwd, String scriptName, bool windows) {
   _is_windows = windows;
   _logResolution("# Current working directory: $cwd");
@@ -141,7 +151,13 @@ String _filePathFromPackageUri(Uri uri) {
           "'$right', not '$wrong'.";
   }
 
-  var path = _entrypoint.resolve('packages/${uri.path}').path;
+  String path;

[Bob Nystrom, 2012/04/20 23:23:20]

Just use "var" here to be consistent with the rest of the file.

+  if (_packageRoot !== null) {
+    path = _packageRoot + uri.path;
+  } else {
+    path = _entrypoint.resolve('packages/${uri.path}').path;
+  }
+
   _logResolution("# Package: $path");
   return path;
 }