[flatbuffers] Enable including by absolute path.

components/subresource_filter/core/common/flat/indexed_ruleset.fbs

Index: components/subresource_filter/core/common/flat/indexed_ruleset.fbs
diff --git a/components/subresource_filter/core/common/flat/indexed_ruleset.fbs b/components/subresource_filter/core/common/flat/indexed_ruleset.fbs
index 91262283f095d79545c6c6c1fda5d06afa07e084..e8e351efb5808d5fe622afe004c31ef5ec08034c 100644
--- a/components/subresource_filter/core/common/flat/indexed_ruleset.fbs
+++ b/components/subresource_filter/core/common/flat/indexed_ruleset.fbs
@@ -2,8 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// TODO(pkalinnikov): Make including by absolute path work.
-include "url_pattern_index.fbs";
+include "components/subresource_filter/core/common/flat/url_pattern_index.fbs";
 
 namespace subresource_filter.flat;