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 bcfd886f3c2bc284e01c379adaaf6c68577f4916..9b1fb2b8ec3c31ae99739c99fae69f95f394332d 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -2065,9 +2065,11 @@ 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)