Fix error handling in POSIX version of the base::File::GetLength.

components/subresource_filter/core/browser/ruleset_service.cc

Index: components/subresource_filter/core/browser/ruleset_service.cc
diff --git a/components/subresource_filter/core/browser/ruleset_service.cc b/components/subresource_filter/core/browser/ruleset_service.cc
index 3a0c5fcb3a4b2992e3bf3e8efc2b06a4231e9f00..6c80bb00e6b429e5cf1ed56112748e087793d2c8 100644
--- a/components/subresource_filter/core/browser/ruleset_service.cc
+++ b/components/subresource_filter/core/browser/ruleset_service.cc
@@ -346,6 +346,8 @@ bool RulesetService::IndexRuleset(base::File unindexed_ruleset_file,
   SCOPED_UMA_HISTOGRAM_TIMER("SubresourceFilter.IndexRuleset.WallDuration");
 
   int64_t unindexed_ruleset_size = unindexed_ruleset_file.GetLength();
+  if (unindexed_ruleset_size < 0)
+    return false;
   CopyingFileInputStream copying_stream(std::move(unindexed_ruleset_file));
   google::protobuf::io::CopyingInputStreamAdaptor zero_copy_stream_adaptor(
       &copying_stream, 4096 /* buffer_size */);