Always pass "allocate: true" when converting URIs to paths.

pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart

Index: pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart
diff --git a/pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart b/pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart
index 19d228a692f8b6c32f6b16af6225fc4f8665ab61..aa51fbf29b7c4e844ffce2a1ec65233731c0581c 100644
--- a/pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart
+++ b/pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.dart
@@ -268,11 +268,8 @@ class _SourceFactoryProxy implements SourceFactory {
   @override
   Source forUri(String absoluteUri) {
     Uri uri = Uri.parse(absoluteUri);
-    if (uri.scheme == 'dart') {
-      return new _SourceProxy(
-          uri, _fileRepository.pathForUri(uri, allocate: true));
-    }
-    return new _SourceProxy(uri, _fileRepository.pathForUri(uri));
+    return new _SourceProxy(
+        uri, _fileRepository.pathForUri(uri, allocate: true));
   }
 
   noSuchMethod(Invocation invocation) => unimplemented();