Move StringToLowerASCII to base namespace

google_apis/gcm/engine/gservices_settings.cc

Index: google_apis/gcm/engine/gservices_settings.cc
diff --git a/google_apis/gcm/engine/gservices_settings.cc b/google_apis/gcm/engine/gservices_settings.cc
index 4e989724b7e7333abd7e4cf53dd64e6ee841d62a..ee342fe3d4af158c5da8410fffa35d88bb459328 100644
--- a/google_apis/gcm/engine/gservices_settings.cc
+++ b/google_apis/gcm/engine/gservices_settings.cc
@@ -196,7 +196,7 @@ std::string GServicesSettings::CalculateDigest(const SettingsMap& settings) {
       reinterpret_cast<const unsigned char*>(&data[0]), data.size(), hash);
   std::string digest =
       kDigestVersionPrefix + base::HexEncode(hash, base::kSHA1Length);
-  digest = StringToLowerASCII(digest);
+  digest = base::StringToLowerASCII(digest);
   return digest;
 }