Add support for resolving symbolic links

pkg/analyzer/lib/file_system/file_system.dart

Index: pkg/analyzer/lib/file_system/file_system.dart
diff --git a/pkg/analyzer/lib/file_system/file_system.dart b/pkg/analyzer/lib/file_system/file_system.dart
index 35816c5bcbd20a41c06783e42a75c68554802f08..8fb602568a7166b7fa57ccfb7d08a97963e6641a 100644
--- a/pkg/analyzer/lib/file_system/file_system.dart
+++ b/pkg/analyzer/lib/file_system/file_system.dart
@@ -54,6 +54,12 @@ abstract class File implements Resource {
   File renameSync(String newPath);
 
   /**
+   * Return a file that refers to the same file as this file, but whose path
+   * does not contain any symbolic links.
+   */
+  File resolveSymbolicLinksSync();
+
+  /**
    * Synchronously write the given [bytes] to the file. The new content will
    * replace any existing content.
    *