Adding MHTML support into Page Load Metrics

chrome/browser/page_load_metrics/browser_page_track_decider.cc

Index: chrome/browser/page_load_metrics/browser_page_track_decider.cc
diff --git a/chrome/browser/page_load_metrics/browser_page_track_decider.cc b/chrome/browser/page_load_metrics/browser_page_track_decider.cc
index f78ed42901ecd41e9d8ae6b7da94dbdd5a36e450..6b52b6b0fb0bae2d275e349281c7661619b2e8c7 100644
--- a/chrome/browser/page_load_metrics/browser_page_track_decider.cc
+++ b/chrome/browser/page_load_metrics/browser_page_track_decider.cc
@@ -52,7 +52,8 @@ int BrowserPageTrackDecider::GetHttpStatusCode() {
 bool BrowserPageTrackDecider::IsHtmlOrXhtmlPage() {
   DCHECK(HasCommitted());
   const std::string& mime_type = web_contents_->GetContentsMimeType();
-  return mime_type == "text/html" || mime_type == "application/xhtml+xml";
+  return mime_type == "text/html" || mime_type == "application/xhtml+xml" ||
+         mime_type == "multipart/related";
 }
 
 }  // namespace page_load_metrics