Implement UMA log throttling for cellular connections

components/metrics/metrics_pref_names.h

Index: components/metrics/metrics_pref_names.h
diff --git a/components/metrics/metrics_pref_names.h b/components/metrics/metrics_pref_names.h
index 15f5acae24917950a471650527de0221fa3bbfaa..5273361199569ddeb9b44d9bfaf6ba7c3a883da3 100644
--- a/components/metrics/metrics_pref_names.h
+++ b/components/metrics/metrics_pref_names.h
@@ -53,6 +53,11 @@ extern const char kStabilityStatsVersion[];
 extern const char kUninstallLaunchCount[];
 extern const char kUninstallMetricsPageLoadCount[];
 extern const char kUninstallMetricsUptimeSec[];
+
+// For measuring data use for throttling UMA log uploads on cellular.
+extern const char kUmaCellDataUse[];
+extern const char kUserCellDataUse[];
+
 }  // namespace prefs
 }  // namespace metrics