update setAnalysisRoots to accept package spec file

pkg/analysis_server/lib/src/context_manager.dart

 // Copyright (c) 2014, 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 context.directory.manager;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:core' hide Resource;
@@ skipping 942 matching lines @@
    *
    * TODO(paulberry): use [addDependency] for tracking all folder disposition
    * dependencies (currently we only use it to track "pub list" dependencies).
    */
   FolderDisposition _computeFolderDisposition(
       Folder folder, void addDependency(String path), File packagespecFile) {
     String packageRoot = normalizedPackageRoots[folder.path];
     if (packageRoot != null) {
       // TODO(paulberry): We shouldn't be using JavaFile here because it
       // makes the code untestable (see dartbug.com/23909).
-      JavaFile packagesDir = new JavaFile(packageRoot);
+      JavaFile packagesDirOrFile = new JavaFile(packageRoot);
       Map<String, List<Folder>> packageMap = new Map<String, List<Folder>>();
-      if (packagesDir.isDirectory()) {
-        for (JavaFile file in packagesDir.listFiles()) {
+      if (packagesDirOrFile.isDirectory()) {
+        for (JavaFile file in packagesDirOrFile.listFiles()) {
           // Ensure symlinks in packages directory are canonicalized
           // to prevent 'type X cannot be assigned to type X' warnings
           String path;
           try {
             path = file.getCanonicalPath();
           } catch (e, s) {
             // Ignore packages that do not exist
             _instrumentationService.logException(e, s);
             continue;
           }
           Resource res = resourceProvider.getResource(path);
           if (res is Folder) {
             packageMap[file.getName()] = <Folder>[res];
           }
         }
         return new PackageMapDisposition(packageMap, packageRoot: packageRoot);
+      } else if (packagesDirOrFile.isFile()) {
+        File packageSpecFile = resourceProvider.getFile(packageRoot);
+        Packages packages = _readPackagespec(packageSpecFile);
+        if (packages != null) {
+          return new PackagesFileDisposition(packages);
+        }
       }
       // The package root does not exist (or is not a folder).  Since
       // [setRoots] ignores any package roots that don't exist (or aren't
       // folders), the only way we should be able to get here is due to a race
       // condition.  In any case, the package root folder is gone, so we can't
       // resolve packages.
       return new NoPackageFolderDisposition(packageRoot: packageRoot);
     } else {
       PackageMapInfo packageMapInfo;
       callbacks.beginComputePackageMap();
@@ skipping 677 matching lines @@
       ResourceProvider resourceProvider) {
     if (packages != null) {
       // Construct package map for the SdkExtUriResolver.
       Map<String, List<Folder>> packageMap = buildPackageMap(resourceProvider);
       return <UriResolver>[new SdkExtUriResolver(packageMap)];
     } else {
       return const <UriResolver>[];
     }
   }
 }