Standardize usage of virtual/override/final specifiers in sync/.

sync/internal_api/attachments/attachment_downloader_impl_unittest.cc

Index: sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
diff --git a/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc b/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
index 96ea5eaef506b2e0d88252d66d642e250ab36554..1d026eb56a5f6de7e01c241b1e18dd332c30057a 100644
--- a/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
+++ b/sync/internal_api/attachments/attachment_downloader_impl_unittest.cc
@@ -154,8 +154,8 @@ class AttachmentDownloaderImplTest : public testing::Test {
 
   AttachmentDownloaderImplTest() : num_completed_downloads_(0) {}
 
-  virtual void SetUp() override;
-  virtual void TearDown() override;
+  void SetUp() override;
+  void TearDown() override;
 
   AttachmentDownloader* downloader() { return attachment_downloader_.get(); }