Introduce a request throttler for limiting requests in mobile NTP.

components/ntp_snippets/pref_names.h

Index: components/ntp_snippets/pref_names.h
diff --git a/components/ntp_snippets/pref_names.h b/components/ntp_snippets/pref_names.h
index 5c432d6f52db03445f32db5c5e3aa0545a540c56..a491bf43733b8f68b9359c001bb719a070720042 100644
--- a/components/ntp_snippets/pref_names.h
+++ b/components/ntp_snippets/pref_names.h
@@ -12,7 +12,12 @@ extern const char kEnableSnippets[];
 
 extern const char kSnippetHosts[];
 
+// Current day for counting NTPSnippetsFetcher requests.
+extern const char kSnippetFetcherQuotaDay[];
+// The count of NTPSnippetsFetcher requests for today, so far.

[tschumann, 2016/07/21 11:37:09]

sorry for being nit-picky: But this constant is a name not a count :-) Would you
mind updating the comment like:
// The pref-name for the NTPSnippetsFetcher requests for today counter.

[i'm unsure if i'm using proper terminology though]

[Marc Treib, 2016/07/21 11:43:50]

I think it's fairly common to have this type of comment on pref names, but
generally you're right, and I don't object to being precise :)
(counter-nit: Leave out the "-" in "pref name")

[jkrcal, 2016/07/21 18:17:57]

Done.

+extern const char kSnippetFetcherQuotaCount[];
+
 }  // namespace prefs
 }  // namespace ntp_snippets
 
-#endif
+#endif  // COMPONENTS_NTP_SNIPPETS_PREF_NAMES_H_