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/fake_prefs.cc b/fake_prefs.cc
index 1df4e30..e26b865 100644
--- a/fake_prefs.cc
+++ b/fake_prefs.cc
@@ -27,8 +27,8 @@
 FakePrefs::PrefType const FakePrefs::PrefConsts<string>::type =
     FakePrefs::PrefType::kString;
 template<>
-string FakePrefs::PrefValue::* const FakePrefs::PrefConsts<string>::member =
-    &FakePrefs::PrefValue::as_str;
+string FakePrefs::PrefValue::* const  // NOLINT(runtime/string), not static str.
+    FakePrefs::PrefConsts<string>::member = &FakePrefs::PrefValue::as_str;
 
 template<>
 FakePrefs::PrefType const FakePrefs::PrefConsts<int64_t>::type =