declare extern template classes sooner

sandbox/linux/bpf_dsl/bpf_dsl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SANDBOX_LINUX_BPF_DSL_BPF_DSL_H_
 #define SANDBOX_LINUX_BPF_DSL_BPF_DSL_H_
 
 #include <stdint.h>
 
 #include <utility>
@@ skipping 69 matching lines @@
 
 // Forward declarations of classes; see below for proper documentation.
 class Elser;
 template <typename T>
 class Caser;
 namespace internal {
 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;
 
 // BoolExpr is an opaque reference to an immutable boolean expression tree.
 typedef scoped_refptr<const internal::BoolExprImpl> BoolExpr;
 
 // Helper class to make writing policies easier.
 class SANDBOX_EXPORT SandboxBPFDSLPolicy : public SandboxBPFPolicy {
  public:
   SandboxBPFDSLPolicy() : SandboxBPFPolicy() {}
@@ skipping 247 matching lines @@
 }
 
 template <typename T>
 ResultExpr Caser<T>::Default(ResultExpr result) const {
   return elser_.Else(result);
 }
 
 }  // 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_