Clean and create output directory when generating docs.

frog/file_system_node.dart

Index: frog/file_system_node.dart
diff --git a/frog/file_system_node.dart b/frog/file_system_node.dart
index 33c2be162d9a2fe736e1c70c0b19af00e3ba5223..0c6f885aa4d1bdf04261441f54b970e981dc5d31 100644
--- a/frog/file_system_node.dart
+++ b/frog/file_system_node.dart
@@ -20,4 +20,64 @@ class NodeFileSystem implements FileSystem {
   bool fileExists(String filename) {
     return path.existsSync(filename);
   }
+
+  void createDirectory(String path, [bool recursive = false]) {
+    if (!recursive) {
+      fs.mkdirSync(path);
+      return;
+    }
+
+    // See how much of the path already exists and how much we need to create.
+    final parts = path.split('/');
+    var existing = '.';
+    var part;
+    for (part = 0; part < parts.length; part++) {
+      final subpath = joinPaths(existing, parts[part]);
+
+      try {
+        final stat = fs.statSync(subpath);
+
+        if (stat.isDirectory()) {
+          existing = subpath;
+        } else {
+          throw 'Cannot create directory $path because $existing exists and ' +
+              'is not a directory.';
+        }
+      } catch (e) {
+        // Ugly hack. We only want to catch ENOENT exceptions from fs.statSync
+        // which means the path we're trying doesn't exist. Since this is coming
+        // from node, we can't check the exception's type.
+        if (e.toString().indexOf('ENOENT', 0) != -1) break;
+
+        // Re-throw any other exceptions.
+        throw e;
+      }
+    }
+
+    // Create the remaining directories.
+    for (; part < parts.length; part++) {
+      existing = joinPaths(existing, parts[part]);
+      fs.mkdirSync(existing);
+    }
+  }
+
+  void removeDirectory(String path, [bool recursive = false]) {
+    if (recursive) {
+      // Remove the contents first.
+      for (final file in fs.readdirSync(path)) {
+        final subpath = joinPaths(path, file);
+        final stat = fs.statSync(subpath);
+
+        if (stat.isDirectory()) {
+          // Recurse into subdirectories.
+          removeDirectory(subpath, recursive: true);
+        } else if (stat.isFile()) {
+          // Try to remove the file.
+          fs.unlinkSync(subpath);
+        }
+      }
+    }
+
+    fs.rmdirSync(path);
+  }
 }