Fail when saving page as MHTML provides information about the cause.

content/browser/frame_host/render_frame_host_impl.h

Index: content/browser/frame_host/render_frame_host_impl.h
diff --git a/content/browser/frame_host/render_frame_host_impl.h b/content/browser/frame_host/render_frame_host_impl.h
index 3d1d6092fa41056576d03ecc478deb38b94f3852..7b4a1f65ce38630eb44fdacc6d64ee516329d925 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -29,6 +29,7 @@
 #include "content/common/accessibility_mode_enums.h"
 #include "content/common/ax_content_node_data.h"
 #include "content/common/content_export.h"
+#include "content/common/download/mhtml_save_status.h"
 #include "content/common/frame.mojom.h"
 #include "content/common/frame_message_enums.h"
 #include "content/common/frame_replication_state.h"
@@ -696,7 +697,7 @@ class CONTENT_EXPORT RenderFrameHostImpl
   void OnDidChangeLoadProgress(double load_progress);
   void OnSerializeAsMHTMLResponse(
       int job_id,
-      bool success,
+      MhtmlSaveStatus save_status,
       const std::set<std::string>& digests_of_uris_of_serialized_resources,
       base::TimeDelta renderer_main_thread_time);
   void OnSelectionChanged(const base::string16& text,