Add support for resolving symbolic links

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 9b95ce8d98762285d24a1647c398181560a04f83..b77114967a1ee5c91e87bf3bcb0034d0fdb1c3ed 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -129,13 +129,17 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   int get modificationStamp {
     try {
-      io.File file = _entry as io.File;
-      return file.lastModifiedSync().millisecondsSinceEpoch;
+      return _file.lastModifiedSync().millisecondsSinceEpoch;
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
+  /**
+   * Return the underlying file being represented by this wrapper.
+   */
+  io.File get _file => _entry as io.File;
+
   @override
   Source createSource([Uri uri]) {
     return new FileSource(this, uri ?? pathContext.toUri(path));
@@ -149,8 +153,7 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   List<int> readAsBytesSync() {
     try {
-      io.File file = _entry as io.File;
-      return file.readAsBytesSync();
+      return _file.readAsBytesSync();
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
@@ -159,8 +162,7 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   String readAsStringSync() {
     try {
-      io.File file = _entry as io.File;
-      return FileBasedSource.fileReadMode(file.readAsStringSync());
+      return FileBasedSource.fileReadMode(_file.readAsStringSync());
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
@@ -169,9 +171,16 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   File renameSync(String newPath) {
     try {
-      io.File file = _entry as io.File;
-      io.File newFile = file.renameSync(newPath);
-      return new _PhysicalFile(newFile);
+      return new _PhysicalFile(_file.renameSync(newPath));
+    } on io.FileSystemException catch (exception) {
+      throw new FileSystemException(exception.path, exception.message);
+    }
+  }
+
+  @override
+  File resolveSymbolicLinksSync() {
+    try {
+      return new _PhysicalFile(new io.File(_file.resolveSymbolicLinksSync()));
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
@@ -183,8 +192,7 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   void writeAsBytesSync(List<int> bytes) {
     try {
-      io.File file = _entry as io.File;
-      file.writeAsBytesSync(bytes);
+      _file.writeAsBytesSync(bytes);
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
@@ -193,8 +201,7 @@ class _PhysicalFile extends _PhysicalResource implements File {
   @override
   void writeAsStringSync(String content) {
     try {
-      io.File file = _entry as io.File;
-      file.writeAsStringSync(content);
+      _file.writeAsStringSync(content);
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }