Adding MHTML support into Page Load Metrics

chrome/browser/page_load_metrics/page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/page_load_metrics_observer.h b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
index 0f742d0ba12766f90aa839989a1d99848af50e9a..1fc5f71b1df296b9c21ad74d0d481da7e6387c1c 100644
--- a/chrome/browser/page_load_metrics/page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 
+#include <string>
+
 #include "base/macros.h"
 #include "base/optional.h"
 #include "chrome/common/page_load_metrics/page_load_timing.h"
@@ -241,6 +243,13 @@ class PageLoadMetricsObserver {
   // fire when the page first loads; for that, listen for OnStart instead.
   virtual ObservePolicy OnShown();
 
+  // Called before OnCommit. The observer should return whether it wishes to
+  // observe navigations whose main resource has MIME type |mine_type|. The
+  // default is to observe HTML and XHTML only. Note that PageLoadTrackers only
+  // track XHTML, HTML, and MHTML (related/multipart).
+  virtual ObservePolicy ShouldObserveMimeType(
+      const std::string& mime_type) const;
+
   // The callbacks below are only invoked after a navigation commits, for
   // tracked page loads. Page loads that don't meet the criteria for being
   // tracked at the time a navigation commits will not receive any of the