declare extern template classes sooner

sandbox/linux/bpf_dsl/bpf_dsl.h

Index: sandbox/linux/bpf_dsl/bpf_dsl.h
diff --git a/sandbox/linux/bpf_dsl/bpf_dsl.h b/sandbox/linux/bpf_dsl/bpf_dsl.h
index bb3557877e6292c9ee5504a9adfb18d933aaa41d..61ca247c69ec3b2a40b3ec5e608eed7e0597fcdc 100644
--- a/sandbox/linux/bpf_dsl/bpf_dsl.h
+++ b/sandbox/linux/bpf_dsl/bpf_dsl.h
@@ -87,6 +87,17 @@ class ResultExprImpl;
 class BoolExprImpl;
 }
 
+}  // namespace bpf_dsl
+}  // namespace sandbox
+
+extern template class SANDBOX_EXPORT
+    scoped_refptr<const sandbox::bpf_dsl::internal::BoolExprImpl>;
+extern template class SANDBOX_EXPORT
+    scoped_refptr<const sandbox::bpf_dsl::internal::ResultExprImpl>;
+
+namespace sandbox {
+namespace bpf_dsl {
+
 // ResultExpr is an opaque reference to an immutable result expression tree.
 typedef scoped_refptr<const internal::ResultExprImpl> ResultExpr;
 
@@ -354,9 +365,4 @@ ResultExpr Caser<T>::Default(ResultExpr result) const {
 }  // namespace bpf_dsl
 }  // namespace sandbox
 
-extern template class SANDBOX_EXPORT
-    scoped_refptr<const sandbox::bpf_dsl::internal::BoolExprImpl>;
-extern template class SANDBOX_EXPORT
-    scoped_refptr<const sandbox::bpf_dsl::internal::ResultExprImpl>;
-
 #endif  // SANDBOX_LINUX_BPF_DSL_BPF_DSL_H_