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/update_manager/variable.h b/update_manager/variable.h
index de8b523..e90d07e 100644
--- a/update_manager/variable.h
+++ b/update_manager/variable.h
@@ -40,7 +40,7 @@
 };
 
 // This class is a base class with the common functionality that doesn't
-// deppend on the variable's type, implemented by all the variables.
+// depend on the variable's type, implemented by all the variables.
 class BaseVariable {
  public:
   // Interface for observing changes on variable value.