Add --package-root option to the compiler.

dart/lib/compiler/implementation/apiimpl.dart

 // Copyright (c) 2012, 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.
 
 #library('leg_apiimpl');
 
 #import('dart:uri');
 
 #import('../compiler.dart', prefix: 'api');
 #import('leg.dart', prefix: 'leg');
 #import('tree/tree.dart', prefix: 'tree');
 #import('elements/elements.dart', prefix: 'elements');
 #import('ssa/tracer.dart', prefix: 'ssa');
 #import('library_map.dart');
 #import('source_file.dart');
 
 class Compiler extends leg.Compiler {
   api.ReadUriFromString provider;
   api.DiagnosticHandler handler;
-  Uri libraryRoot;
-  Uri packageRoot;
+  final Uri libraryRoot;
+  final Uri packageRoot;
   List<String> options;
   bool mockableLibraryUsed = false;
 
-  Compiler(this.provider, this.handler, this.libraryRoot, List<String> options)
+  Compiler(this.provider, this.handler, this.libraryRoot, this.packageRoot,
+           List<String> options)
     : this.options = options,
       super(
           tracer: new ssa.HTracer(),
           enableTypeAssertions: options.indexOf('--enable-checked-mode') != -1,
           emitJavascript: options.indexOf('--output-type=dart') == -1);
 
   elements.LibraryElement scanBuiltinLibrary(String path) {
     Uri uri = libraryRoot.resolve(DART2JS_LIBRARY_MAP[path]);
     elements.LibraryElement library = scanner.loadLibrary(uri, null);
     return library;
@@ skipping 38 matching lines @@
       // TODO(ahe): Get rid of mockableLibraryUsed when test.dart
       // supports this use case better.
       mockableLibraryUsed = true;
     }
     return libraryRoot.resolve(path);
   }
 
   translatePackageUri(Uri uri, tree.Node node) => packageRoot.resolve(uri.path);
 
   bool run(Uri uri) {
-    try {
-      packageRoot = uri.resolve('packages/');
-      bool success = super.run(uri);
-      for (final task in tasks) {
-        log('${task.name} took ${task.timing}msec');
-      }
-      return success;
-    } finally {
-      packageRoot = null;
+    bool success = super.run(uri);
+    for (final task in tasks) {
+      log('${task.name} took ${task.timing}msec');
     }
+    return success;
   }
 
   void reportDiagnostic(leg.SourceSpan span, String message, bool fatal) {
     if (span === null) {
       handler(null, null, null, message, fatal);
     } else {
       handler(span.uri, span.begin, span.end, message, fatal);
     }
   }
 
   bool get isMockCompilation() {
     return mockableLibraryUsed
       && (options.indexOf('--allow-mock-compilation') !== -1);
   }
 }