Fix UnindexedRulesetWriter finishing.

components/subresource_filter/core/common/unindexed_ruleset.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/subresource_filter/core/common/unindexed_ruleset.h"
 
 #include "base/numerics/safe_conversions.h"
 
 namespace subresource_filter {
 
@@ skipping 33 matching lines @@
   pending_chunk_.add_url_rules()->CopyFrom(rule);
   if (pending_chunk_.url_rules_size() >= max_rules_per_chunk_) {
     DCHECK_EQ(pending_chunk_.url_rules_size(), max_rules_per_chunk_);
     return WritePendingChunk();
   }
   return true;
 }
 
 bool UnindexedRulesetWriter::Finish() {
   DCHECK(!had_error());
-  return !pending_chunk_.url_rules_size() || WritePendingChunk();
+  const bool success = !pending_chunk_.url_rules_size() || WritePendingChunk();
+  if (success)
+    coded_stream_.Trim();
+  return success;
 }
 
 bool UnindexedRulesetWriter::WritePendingChunk() {
   DCHECK(!had_error());
   DCHECK_GT(pending_chunk_.url_rules_size(), 0);
 
   proto::FilteringRules chunk;
   chunk.Swap(&pending_chunk_);
   coded_stream_.WriteVarint32(base::checked_cast<uint32_t>(chunk.ByteSize()));
   return !had_error() && chunk.SerializeToCodedStream(&coded_stream_);
 }
 
 }  // namespace subresource_filter