Fix UnindexedRulesetWriter finishing.

components/subresource_filter/core/common/unindexed_ruleset_unittest.cc

Index: components/subresource_filter/core/common/unindexed_ruleset_unittest.cc
diff --git a/components/subresource_filter/core/common/unindexed_ruleset_unittest.cc b/components/subresource_filter/core/common/unindexed_ruleset_unittest.cc
index 5c093b3aa25609c902a6cff839192c75ec88bd3c..89eb989b06d6b79cb98d47e6f066f50ec6b79f9e 100644
--- a/components/subresource_filter/core/common/unindexed_ruleset_unittest.cc
+++ b/components/subresource_filter/core/common/unindexed_ruleset_unittest.cc
@@ -140,6 +140,24 @@ TEST(UnindexedRulesetTest, EmptyRuleset) {
   EXPECT_TRUE(IsRulesetValid(builder.ruleset_contents(), builder.url_rules()));
 }
 
+// The following test addresses a bug, that the UnindexedRulesetWriter didn't

[engedy, 2016/08/26 15:43:17]

Let's just call a spade a spade + phrasing suggestion.

// Regression test for a bug where the ... resulting in the output having ...

[pkalinnikov1, 2016/08/26 16:29:47]

Done.

+// trim the output coded stream on Finish, causing the output had some extra
+// uninitialized bytes at the end.
+TEST(UnindexedRulesetTest, EmptyRulesetRegression) {
+  size_t contents_size_after_finish = 0;
+  std::string contents;
+
+  {
+    google::protobuf::io::StringOutputStream output(&contents);
+    UnindexedRulesetWriter ruleset_writer(&output);
+    EXPECT_TRUE(ruleset_writer.Finish());

[engedy, 2016/08/26 15:43:17]

Hang on, is this going to allocate a single byte of buffer if we don't write
anything?

[pkalinnikov1, 2016/08/26 16:29:47]

No, the size of the contents will be 0. I could add EXPECT_EQ(0, size), but this
would make the test depend on the wire format. E.g., if we add a fixed header at
the beginning of UnindexedRuleset, the size will become sizeof(Header). Should I
leave this code as is?

+    contents_size_after_finish = contents.size();
+  }
+
+  // The |contents| shouldn't be resized after writer/stream destruction.
+  EXPECT_EQ(contents_size_after_finish, contents.size());
+}
+
 TEST(UnindexedRulesetTest, OneUrlRule) {
   UnindexedRulesetTestBuilder builder;
   EXPECT_TRUE(builder.AddUrlRule(UrlPattern("example.com"),