Add support for cross-session storage

pkg/analyzer/lib/file_system/physical_file_system.dart

Index: pkg/analyzer/lib/file_system/physical_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index 55c778e76dc8f056a8e58f05de0ec9ce792d92ee..bf74ec54be8fb8929c9c7ac5597572fa9204a586 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -22,6 +22,12 @@ class PhysicalResourceProvider implements ResourceProvider {
   static final PhysicalResourceProvider INSTANCE =
       new PhysicalResourceProvider._();
 
+  /**
+   * The name of the directory containing plugin specific subfolders used to
+   * store data across sessions.
+   */
+  static final String SERVER_DIR = "dartServer";

[Paul Berry, 2014/10/07 16:50:36]

On Mac and Unix it's conventional to name these directories with a leading "."
(e.g. ".pub-cache") so that they are hidden.  I'm not sure what the convention
is on Windows.

[Brian Wilkerson, 2014/10/07 16:57:51]

Done

+
   PhysicalResourceProvider._();
 
   @override
@@ -37,6 +43,28 @@ class PhysicalResourceProvider implements ResourceProvider {
       return new _PhysicalFile(file);
     }
   }
+
+  @override
+  Folder getStateLocation(String pluginId) {
+    String home;
+    if (io.Platform.isWindows) {
+      home = io.Platform.environment['LOCALAPPDATA'];
+    } else {
+      home = io.Platform.environment['HOME'];
+    }
+    if (home != null && io.FileSystemEntity.isDirectorySync(home)) {
+      StringBuffer buffer = new StringBuffer();
+      buffer.write(home);
+      buffer.write(pathContext.separator);
+      buffer.write(SERVER_DIR);
+      buffer.write(pathContext.separator);
+      buffer.write(pluginId);

[Paul Berry, 2014/10/07 16:50:36]

IMHO it reads a lot nicer to construct paths using path.join, e.g.:

  io.Directory directory = new io.Directory(join(home, SERVER_DIR, pluginId));

[Brian Wilkerson, 2014/10/07 16:57:51]

Done

+      io.Directory directory = new io.Directory(buffer.toString());
+      directory.createSync(recursive: true);
+      return new _PhysicalFolder(directory);
+    }
+    return null;
+  }
 }