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 <[email protected]>
Commit-Queue: Alex Vakulenko <[email protected]>
Tested-by: Alex Vakulenko <[email protected]>
diff --git a/file_writer.h b/file_writer.h
index e2083c3..70d4778 100644
--- a/file_writer.h
+++ b/file_writer.h
@@ -31,7 +31,7 @@
   virtual int Open(const char* path, int flags, mode_t mode) = 0;
 
   // Wrapper around write. Returns true if all requested bytes
-  // were written, or false on any error, reguardless of progress.
+  // were written, or false on any error, regardless of progress.
   virtual bool Write(const void* bytes, size_t count) = 0;
 
   // Same as the Write method above but returns a detailed |error| code