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.h b/delta_performer.h
index 189fe3a..c663208 100644
--- a/delta_performer.h
+++ b/delta_performer.h
@@ -210,7 +210,7 @@
       const DeltaArchiveManifest_InstallOperation& op);
 
   // Verifies that the expected source partition hashes (if present) match the
-  // hashes for the current partitions. Returns true if there're no expected
+  // hashes for the current partitions. Returns true if there are no expected
   // hashes in the payload (e.g., if it's a new-style full update) or if the
   // hashes match; returns false otherwise.
   bool VerifySourcePartitions();