Make headless_shell target compile for Windows

headless/public/headless_shell.h

Index: headless/public/headless_shell.h
diff --git a/headless/public/headless_shell.h b/headless/public/headless_shell.h
index f083d2030c1057d70fdfdd4ccd364e671c505f7a..0fd9066a80d5ef01842a9decea1c10e04b67503c 100644
--- a/headless/public/headless_shell.h
+++ b/headless/public/headless_shell.h
@@ -11,8 +11,7 @@ namespace headless {
 
 // Start the Headless Shell application. Intended to be called early in main().
 // Returns the exit code for the process.
-int HEADLESS_EXPORT HeadlessShellMain(int argc, const char** argv);
-
+HEADLESS_EXPORT int HeadlessShellMain(int argc, const char** argv);
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_HEADLESS_SHELL_H_