Add UMA histograms to MHTML save operations.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index ade16ba1826e7d0dcfc125c7fbceaae55a57be40..2b758e3da02ec9f7c8c0a42b83548d1da74652d2 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -2082,9 +2082,11 @@ void RenderFrameHostImpl::OnDidChangeLoadProgress(double load_progress) {
 void RenderFrameHostImpl::OnSerializeAsMHTMLResponse(
     int job_id,
     bool success,
-    const std::set<std::string>& digests_of_uris_of_serialized_resources) {
+    const std::set<std::string>& digests_of_uris_of_serialized_resources,
+    base::TimeDelta renderer_main_thread_time) {
   MHTMLGenerationManager::GetInstance()->OnSerializeAsMHTMLResponse(
-      this, job_id, success, digests_of_uris_of_serialized_resources);
+      this, job_id, success, digests_of_uris_of_serialized_resources,
+      renderer_main_thread_time);
 }
 
 #if defined(USE_EXTERNAL_POPUP_MENU)