Pepper: Add MonitorIsExternal function to PPB_Flash_DRM.

ppapi/cpp/private/flash_drm.h

Index: ppapi/cpp/private/flash_drm.h
diff --git a/ppapi/cpp/private/flash_drm.h b/ppapi/cpp/private/flash_drm.h
index 45ecde8b9a4c20e55742b86e92f5ae4de28b814c..2edddac1d526e2aed85e12d700cb163952362297 100644
--- a/ppapi/cpp/private/flash_drm.h
+++ b/ppapi/cpp/private/flash_drm.h
@@ -27,6 +27,10 @@ class DRM : public Resource {
   bool GetHmonitor(int64_t* hmonitor);
   // Returns the voucher file as a FileRef or an invalid resource on failure.
   int32_t GetVoucherFile(const CompletionCallbackWithOutput<FileRef>& callback);
+  // On success, returns a value indicating if the monitor associated with the
+  // current plugin instance is external.
+  int32_t MonitorIsExternal(
+      const CompletionCallbackWithOutput<PP_Bool>& callback);
 };
 
 }  // namespace flash