Update all users of base::Version to explicitly specify the namespace, and clean up the header.

extensions/common/extension.cc

Index: extensions/common/extension.cc
diff --git a/extensions/common/extension.cc b/extensions/common/extension.cc
index 640e96b6da03a22f51adef1e68f7b5723596b682..2bab533efa734580f98f79ecd52b48ead6cc3995 100644
--- a/extensions/common/extension.cc
+++ b/extensions/common/extension.cc
@@ -590,7 +590,7 @@ bool Extension::LoadVersion(base::string16* error) {
     *error = 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 = ASCIIToUTF16(errors::kInvalidVersion);
     return false;