Revert of base: Remove using:: declaration from version.h header.

components/variations/processed_study.cc

Index: components/variations/processed_study.cc
diff --git a/components/variations/processed_study.cc b/components/variations/processed_study.cc
index c8966ecbd79c5c64cb4933d81f4d9ff4da1924fc..5f065d8e1e88ac19a6034581eb49780a775d132e 100644
--- a/components/variations/processed_study.cc
+++ b/components/variations/processed_study.cc
@@ -26,13 +26,13 @@
     return false;
   }
   if (study.filter().has_min_version() &&
-      !base::Version::IsValidWildcardString(study.filter().min_version())) {
+      !Version::IsValidWildcardString(study.filter().min_version())) {
     DVLOG(1) << study.name() << " has invalid min version: "
              << study.filter().min_version();
     return false;
   }
   if (study.filter().has_max_version() &&
-      !base::Version::IsValidWildcardString(study.filter().max_version())) {
+      !Version::IsValidWildcardString(study.filter().max_version())) {
     DVLOG(1) << study.name() << " has invalid max version: "
              << study.filter().max_version();
     return false;