Fix missing HEADLESS_EXPORT defines

headless/public/util/expedited_dispatcher.h

Index: headless/public/util/expedited_dispatcher.h
diff --git a/headless/public/util/expedited_dispatcher.h b/headless/public/util/expedited_dispatcher.h
index 61062c4d51d50e929e2bc04062081f36563f7077..80579d2d04aae6d3352f35419ec6f234b580ce8c 100644
--- a/headless/public/util/expedited_dispatcher.h
+++ b/headless/public/util/expedited_dispatcher.h
@@ -8,6 +8,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
+#include "headless/public/headless_export.h"
 #include "headless/public/util/url_request_dispatcher.h"
 #include "net/base/net_errors.h"
 
@@ -17,7 +18,7 @@ class ManagedDispatchURLRequestJob;
 
 // This class dispatches calls to OnHeadersComplete and OnStartError
 // immediately sacrificing determinism for performance.
-class ExpeditedDispatcher : public URLRequestDispatcher {
+class HEADLESS_EXPORT ExpeditedDispatcher : public URLRequestDispatcher {
  public:
   explicit ExpeditedDispatcher(
       scoped_refptr<base::SingleThreadTaskRunner> io_thread_task_runner);