update_engine: fixed remaining linter and some spelling errors

Fixed remaining errors from cpplint as well as some spelling errors
mostly in comments.

BUG=None
TEST=FEATURES=test emerge-link update_engine

Change-Id: I484988ab846ac5a3c68c016ddccfb247f225ec27
Reviewed-on: https://chromium-review.googlesource.com/208897
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/delta_performer_unittest.cc b/delta_performer_unittest.cc
index c2e4667..d68aa25 100644
--- a/delta_performer_unittest.cc
+++ b/delta_performer_unittest.cc
@@ -1264,7 +1264,7 @@
   //
   //  1. Whether it's an official build; and
   //  2. Whether the Public RSA key to be used is in the root filesystem; and
-  //  3. Whether the reponse has a public key
+  //  3. Whether the response has a public key
   //
   // We test all eight combinations to ensure that we only use the
   // public key in the response if