Add basename and dirname to FileSystemEntity (flutter#15)

Author: tvolkert

lib/src/backends/chroot/chroot_file_system_entity.dart

@@ -14,6 +14,12 @@ abstract class _ChrootFileSystemEntity<T extends FileSystemEntity,
 
   _ChrootFileSystemEntity(this.fileSystem, this.path);
 
+  @override
+  String get dirname => fileSystem.path.dirname(path);
+
+  @override
+  String get basename => fileSystem.path.basename(path);
+
   @override
   D get delegate => getDelegate();
 

lib/src/backends/local/local_file_system_entity.dart

@@ -14,6 +14,12 @@ abstract class _LocalFileSystemEntity<T extends FileSystemEntity,
 
   _LocalFileSystemEntity(this.fileSystem, this.delegate);
 
+  @override
+  String get dirname => fileSystem.path.dirname(path);
+
+  @override
+  String get basename => fileSystem.path.basename(path);
+
   @override
   Directory wrapDirectory(io.Directory delegate) =>
       new _LocalDirectory(fileSystem, delegate);

lib/src/backends/memory/memory_file_system_entity.dart

@@ -21,10 +21,10 @@ abstract class _MemoryFileSystemEntity implements FileSystemEntity {
 
   _MemoryFileSystemEntity(this.fileSystem, this.path);
 
-  /// Gets the part of this entity's path before the last separator.
+  @override
   String get dirname => fileSystem.path.dirname(path);
 
-  /// Gets the part of this entity's path after the last separator.
+  @override
   String get basename => fileSystem.path.basename(path);
 
   /// Returns the expected type of this entity, which may differ from the type

lib/src/forwarding/forwarding_file_system_entity.dart

@@ -85,4 +85,10 @@ abstract class ForwardingFileSystemEntity<T extends FileSystemEntity,
 
   @override
   String get path => delegate.path;
+
+  @override
+  String get basename => fileSystem.path.basename(path);
+
+  @override
+  String get dirname => fileSystem.path.dirname(path);
 }

lib/src/interface/file_system_entity.dart

@@ -9,6 +9,27 @@ abstract class FileSystemEntity implements io.FileSystemEntity {
   /// Returns the file system responsible for this entity.
   FileSystem get fileSystem;
 
+  /// Gets the part of this entity's path after the last separator.
+  ///
+  ///     context.basename('path/to/foo.dart'); // -> 'foo.dart'
+  ///     context.basename('path/to');          // -> 'to'
+  ///
+  /// Trailing separators are ignored.
+  ///
+  ///     context.basename('path/to/'); // -> 'to'
+  String get basename;
+
+  /// Gets the part of this entity's path before the last separator.
+  ///
+  ///     context.dirname('path/to/foo.dart'); // -> 'path/to'
+  ///     context.dirname('path/to');          // -> 'path'
+  ///     context.dirname('foo.dart');         // -> '.'
+  ///
+  /// Trailing separators are ignored.
+  ///
+  ///     context.dirname('path/to/'); // -> 'path'
+  String get dirname;
+
   // Override method definitions to codify the return type covariance.
   @override
   Future<FileSystemEntity> delete({bool recursive: false});