Replace ToLower calls to the new format

components/language_usage_metrics/language_usage_metrics.cc

Index: components/language_usage_metrics/language_usage_metrics.cc
diff --git a/components/language_usage_metrics/language_usage_metrics.cc b/components/language_usage_metrics/language_usage_metrics.cc
index 190507fb3997e7487d82897183c7698634835c49..ac44499c53ddea510f40d07e4863f4165e18638f 100644
--- a/components/language_usage_metrics/language_usage_metrics.cc
+++ b/components/language_usage_metrics/language_usage_metrics.cc
@@ -42,8 +42,7 @@ int LanguageUsageMetrics::ToLanguageCode(const std::string& locale) {
   if (!parts.GetNext())
     return 0;
 
-  std::string language_part = parts.token();
-  base::StringToLowerASCII(&language_part);
+  std::string language_part = base::ToLowerASCII(parts.token());
 
   int language_code = 0;
   for (std::string::iterator it = language_part.begin();