add missing CONTENT_EXPORT

content/common/gamepad_seqlock.h

Index: content/common/gamepad_seqlock.h
diff --git a/content/common/gamepad_seqlock.h b/content/common/gamepad_seqlock.h
index 811aeca387924a59d5d830de17b5826985ec6ace..35f51e58d39d6ea6ef4401fca9441907788e16b8 100644
--- a/content/common/gamepad_seqlock.h
+++ b/content/common/gamepad_seqlock.h
@@ -7,6 +7,7 @@
 
 #include "base/atomicops.h"
 #include "base/threading/platform_thread.h"
+#include "content/common/content_export.h"
 
 namespace content {
 
@@ -27,7 +28,7 @@ namespace content {
 // garbage, or indices could be out of range. Probably the only suitable thing
 // to do during the read loop is to make a copy of the data, and operate on it
 // only after the read was found to be consistent.
-class GamepadSeqLock {
+class CONTENT_EXPORT GamepadSeqLock {
  public:
   GamepadSeqLock();
   base::subtle::Atomic32 ReadBegin();