Move more string_util functions to base namespace.

components/gcm_driver/instance_id/instance_id_driver_unittest.cc

Index: components/gcm_driver/instance_id/instance_id_driver_unittest.cc
diff --git a/components/gcm_driver/instance_id/instance_id_driver_unittest.cc b/components/gcm_driver/instance_id/instance_id_driver_unittest.cc
index af63866682c2cf4040321db2d8ae3ef430cab2e9..9474d2462ab5d91598a17c64425427b4651d5c5d 100644
--- a/components/gcm_driver/instance_id/instance_id_driver_unittest.cc
+++ b/components/gcm_driver/instance_id/instance_id_driver_unittest.cc
@@ -32,7 +32,8 @@ bool VerifyInstanceID(const std::string& str) {
 
   // Checks if it is URL-safe base64 encoded.
   for (auto ch : str) {
-    if (!IsAsciiAlpha(ch) && !IsAsciiDigit(ch) && ch != '_' && ch != '-')
+    if (!base::IsAsciiAlpha(ch) && !base::IsAsciiDigit(ch) &&
+        ch != '_' && ch != '-')
       return false;
   }
   return true;