Adding MHTML support into Page Load Metrics

chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.cc
index 4b5b431d0629c7146668e8a856fa3e51ac45cfce..0475ec583ec0799a0dd6d0d78ae423cdbbf00421 100644
--- a/chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.cc
+++ b/chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.cc
@@ -4,8 +4,6 @@
 
 #include "chrome/browser/page_load_metrics/observers/previews_page_load_metrics_observer.h"
 
-#include <string>
-
 #include "base/optional.h"
 #include "base/time/time.h"
 #include "chrome/browser/page_load_metrics/page_load_metrics_util.h"
@@ -50,6 +48,18 @@ PreviewsPageLoadMetricsObserver::OnCommit(
              : STOP_OBSERVING;
 }
 
+page_load_metrics::PageLoadMetricsObserver::ObservePolicy
+PreviewsPageLoadMetricsObserver::ShouldObserveMimeType(
+    const std::string& mime_type) const {
+  // On top of base-supported types, support MHTML. Offline previews are served
+  // as MHTML (multipart/related).
+  return PageLoadMetricsObserver::ShouldObserveMimeType(mime_type) ==
+                     CONTINUE_OBSERVING ||
+                 mime_type == "multipart/related"
+             ? CONTINUE_OBSERVING
+             : STOP_OBSERVING;
+}
+
 void PreviewsPageLoadMetricsObserver::OnDomContentLoadedEventStart(
     const page_load_metrics::PageLoadTiming& timing,
     const page_load_metrics::PageLoadExtraInfo& info) {