Fix some extern usage in .cc files.

content/common/sandbox_init_mac.cc

Index: content/common/sandbox_init_mac.cc
diff --git a/content/common/sandbox_init_mac.cc b/content/common/sandbox_init_mac.cc
index 2597a75f14d8da8768168c426dd773f79b7684f7..c49aa80685eaea32cef5fa90c07e8f57d24fac86 100644
--- a/content/common/sandbox_init_mac.cc
+++ b/content/common/sandbox_init_mac.cc
@@ -2,13 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "content/public/common/sandbox_init.h"
+#include "content/common/sandbox_init_mac.h"
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "content/common/sandbox_mac.h"
 #include "content/public/common/content_switches.h"
+#include "content/public/common/sandbox_init.h"
 
 namespace content {
 
@@ -82,7 +83,4 @@ bool BrokerDuplicateSharedMemoryHandle(
   return base::SharedMemory::IsHandleValid(*target_handle);
 }
 
-extern const char kBootstrapPortNameForNPAPIPlugins[] =
-    "org.chromium.sandbox.real_bootstrap_server";
-
 }  // namespace content