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/error_code.h b/error_code.h
index 5f3a2cb..a9bfc2d 100644
--- a/error_code.h
+++ b/error_code.h
@@ -5,7 +5,7 @@
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_ERROR_CODE_H_
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_ERROR_CODE_H_
 
-#include <ostream>
+#include <ostream>  // NOLINT(readability/streams)
 
 namespace chromeos_update_engine {