fix PathObserver to avoid try+catch

pkg/observe/lib/transform.dart

Index: pkg/observe/lib/transform.dart
diff --git a/pkg/observe/lib/transform.dart b/pkg/observe/lib/transform.dart
index ede5a0d92580572db72a039a6fb2dbc8113e9bc1..5e261c02b49b641fe30f36867373bd9a9ca3a9c5 100644
--- a/pkg/observe/lib/transform.dart
+++ b/pkg/observe/lib/transform.dart
@@ -256,11 +256,11 @@ void _mixinObservable(ClassDeclaration cls, TextEditTransaction code) {
 }
 
 SimpleIdentifier _getSimpleIdentifier(Identifier id) =>
-    id is PrefixedIdentifier ? (id as PrefixedIdentifier).identifier : id;
+    id is PrefixedIdentifier ? id.identifier : id;
 
 
 bool _hasKeyword(Token token, Keyword keyword) =>
-    token is KeywordToken && (token as KeywordToken).keyword == keyword;
+    token is KeywordToken && token.keyword == keyword;
 
 String _getOriginalCode(TextEditTransaction code, ASTNode node) =>
     code.original.substring(node.offset, node.end);