Adding MHTML support into Page Load Metrics

chrome/browser/page_load_metrics/page_load_tracker.cc

Index: chrome/browser/page_load_metrics/page_load_tracker.cc
diff --git a/chrome/browser/page_load_metrics/page_load_tracker.cc b/chrome/browser/page_load_metrics/page_load_tracker.cc
index 6f161e9fa3d7913d4eba92157bb0c03939b0b0c4..77b33fee3ff53dfce476c2c53fbb64597b3f644d 100644
--- a/chrome/browser/page_load_metrics/page_load_tracker.cc
+++ b/chrome/browser/page_load_metrics/page_load_tracker.cc
@@ -18,6 +18,7 @@
 #include "chrome/common/page_load_metrics/page_load_timing.h"
 #include "content/public/browser/navigation_details.h"
 #include "content/public/browser/navigation_handle.h"
+#include "content/public/browser/web_contents.h"
 #include "content/public/common/browser_side_navigation_policy.h"
 #include "ui/base/page_transition_types.h"
 
@@ -446,6 +447,10 @@ void PageLoadTracker::Commit(content::NavigationHandle* navigation_handle) {
   page_transition_ = navigation_handle->GetPageTransition();
   user_initiated_info_.user_gesture = navigation_handle->HasUserGesture();
 
+  INVOKE_AND_PRUNE_OBSERVERS(

[Bryan McQuade, 2017/02/21 18:50:15]

ah, nice, this actually works very well. i like this approach.

+      observers_, ShouldObserveMimeType,
+      navigation_handle->GetWebContents()->GetContentsMimeType());
+
   INVOKE_AND_PRUNE_OBSERVERS(observers_, OnCommit, navigation_handle);
   LogAbortChainHistograms(navigation_handle);
 }