Fix UnindexedRulesetWriter finishing.

This CL fixes the bug where UnindexedRulesetWriter doesn't trim the
CodedOutputStream on Finish, resulting in the output having some extra
uninitialized bytes at the end.

BUG=609747

Review-Url: https://codereview.chromium.org/2279803002
Cr-Commit-Position: refs/heads/master@{#414762}

components/subresource_filter/core/browser/ruleset_service.cc

@@ -300,7 +300,7 @@ bool RulesetService::IndexRuleset(base::File unindexed_ruleset_file,
       "SubresourceFilter.IndexRuleset.NumUnsupportedRules",
       num_unsupported_rules);
 
-  return zero_copy_stream_adaptor.ByteCount() == unindexed_ruleset_size;
+  return reader.num_bytes_read() == unindexed_ruleset_size;
 }
 
 // static

components/subresource_filter/core/common/unindexed_ruleset.cc

@@ -51,7 +51,10 @@ bool UnindexedRulesetWriter::AddUrlRule(const proto::UrlRule& rule) {
 
 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() {

components/subresource_filter/core/common/unindexed_ruleset.h

@@ -42,6 +42,9 @@ class UnindexedRulesetReader {
   // ReadNextChunk is undefined befaviour.
   bool ReadNextChunk(proto::FilteringRules* chunk);
 
+  // Returns how many bytes of the |stream| have been consumed.
+  int num_bytes_read() const { return coded_stream_.CurrentPosition(); }
+
  private:
   google::protobuf::io::CodedInputStream coded_stream_;
 

components/subresource_filter/core/common/unindexed_ruleset_unittest.cc

@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/macros.h"
+#include "base/numerics/safe_conversions.h"
 #include "base/strings/string_number_conversions.h"
 #include "components/subresource_filter/core/common/proto/rules.pb.h"
 #include "components/subresource_filter/core/common/url_pattern.h"
@@ -122,6 +123,10 @@ bool IsRulesetValid(const std::string& ruleset_contents,
     read_rules.insert(read_rules.end(), chunk.url_rules().begin(),
                       chunk.url_rules().end());
   }
+  if (base::checked_cast<size_t>(reader.num_bytes_read()) !=
+      ruleset_contents.size()) {
+    return false;
+  }
 
   if (expected_url_rules.size() != read_rules.size())
     return false;