update_engine: fixed warnings from cpplint

Fixed all the cpplint warnings in update engine.

BUG=None
TEST=Unit tests still pass.

Change-Id: I285ae858eec8abe0b26ff203b99a42a200ceb71c
Reviewed-on: https://chromium-review.googlesource.com/204027
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/payload_generator/metadata.cc b/payload_generator/metadata.cc
index f0c9238..d0ab82c 100644
--- a/payload_generator/metadata.cc
+++ b/payload_generator/metadata.cc
@@ -425,7 +425,7 @@
   return true;
 }
 
-}  // namespace {}
+}  // namespace
 
 // Reads metadata from old image and new image and determines
 // the smallest way to encode the metadata for the diff.