Make `chrome` target build without unused data members on Linux.

chrome/browser/extensions/api/messaging/native_process_launcher.cc

Index: chrome/browser/extensions/api/messaging/native_process_launcher.cc
diff --git a/chrome/browser/extensions/api/messaging/native_process_launcher.cc b/chrome/browser/extensions/api/messaging/native_process_launcher.cc
index a60b166b035cf6c462e089cbb5591f46ee925ba0..224664c471169627d0636d96ac7cde283c80f3e7 100644
--- a/chrome/browser/extensions/api/messaging/native_process_launcher.cc
+++ b/chrome/browser/extensions/api/messaging/native_process_launcher.cc
@@ -78,8 +78,10 @@ class NativeProcessLauncherImpl : public NativeProcessLauncher {
 
     bool allow_user_level_hosts_;
 
+#if defined(OS_WIN)
     // Handle of the native window corresponding to the extension.
     intptr_t window_handle_;
+#endif // OS_WIN
 
     DISALLOW_COPY_AND_ASSIGN(Core);
   };
@@ -92,9 +94,11 @@ class NativeProcessLauncherImpl : public NativeProcessLauncher {
 NativeProcessLauncherImpl::Core::Core(bool allow_user_level_hosts,
                                       intptr_t window_handle)
     : detached_(false),
-      allow_user_level_hosts_(allow_user_level_hosts),
-      window_handle_(window_handle) {
-}
+      allow_user_level_hosts_(allow_user_level_hosts)
+#if defined(OS_WIN)
+      , window_handle_(window_handle)
+#endif // OS_WIN
+{}
 
 NativeProcessLauncherImpl::Core::~Core() {
   DCHECK(detached_);