tools/gn: Add out-of-line copy ctors for complex classes.

tools/gn/label.cc

 // Copyright (c) 2013 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.
 
 #include "tools/gn/label.h"
 
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 #include "build/build_config.h"
 #include "tools/gn/err.h"
@@ skipping 196 matching lines @@
       toolchain_dir_(toolchain_dir) {
   name_.assign(name.data(), name.size());
   toolchain_name_.assign(toolchain_name.data(), toolchain_name.size());
 }
 
 Label::Label(const SourceDir& dir, const base::StringPiece& name)
     : dir_(dir) {
   name_.assign(name.data(), name.size());
 }
 
+Label::Label(const Label& other) = default;
+
 Label::~Label() {
 }
 
 // static
 Label Label::Resolve(const SourceDir& current_dir,
                      const Label& current_toolchain,
                      const Value& input,
                      Err* err) {
   Label ret;
   if (input.type() != Value::STRING) {
@@ skipping 44 matching lines @@
   }
   return ret;
 }
 
 std::string Label::GetUserVisibleName(const Label& default_toolchain) const {
   bool include_toolchain =
       default_toolchain.dir() != toolchain_dir_ ||
       default_toolchain.name() != toolchain_name_;
   return GetUserVisibleName(include_toolchain);
 }