Consistently use namespaced base::Version in extensions code.

extensions/common/extension.cc

Index: extensions/common/extension.cc
diff --git a/extensions/common/extension.cc b/extensions/common/extension.cc
index fd77aa0ab207fd19af25a92c73d496578015c6ed..2f5e2d653e2996f575147f8c36d8358da6965c12 100644
--- a/extensions/common/extension.cc
+++ b/extensions/common/extension.cc
@@ -579,7 +579,7 @@ bool Extension::LoadVersion(base::string16* error) {
     *error = base::ASCIIToUTF16(errors::kInvalidVersion);
     return false;
   }
-  version_.reset(new Version(version_str));
+  version_.reset(new base::Version(version_str));
   if (!version_->IsValid() || version_->components().size() > 4) {
     *error = base::ASCIIToUTF16(errors::kInvalidVersion);
     return false;