Add support for tracking loading behavior of child frames.

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 f6d8e104267d9e300da4da1dadab01eac9151889..d7f9a213ae38f05cbf2f028b0f4c765c54257182 100644
--- a/chrome/browser/page_load_metrics/page_load_tracker.cc
+++ b/chrome/browser/page_load_metrics/page_load_tracker.cc
@@ -506,6 +506,22 @@ void PageLoadTracker::NotifyClientRedirectTo(
   }
 }
 
+void PageLoadTracker::UpdateChildMetadata(
+    const PageLoadMetadata& child_metadata) {
+  // Merge the child loading behavior flags with any we've already observed,
+  // possibly from other child frames.
+  const int last_child_loading_behavior_flags =
+      child_frame_metadata_.behavior_flags;
+  child_frame_metadata_.behavior_flags |= child_metadata.behavior_flags;
+  if (last_child_loading_behavior_flags == child_frame_metadata_.behavior_flags)
+    return;
+
+  PageLoadExtraInfo extra_info(ComputePageLoadExtraInfo());
+  for (const auto& observer : observers_) {
+    observer->OnLoadingBehaviorObserved(extra_info);
+  }
+}
+
 bool PageLoadTracker::UpdateTiming(const PageLoadTiming& new_timing,
                                    const PageLoadMetadata& new_metadata) {
   // Throw away IPCs that are not relevant to the current navigation.
@@ -619,7 +635,7 @@ PageLoadExtraInfo PageLoadTracker::ComputePageLoadExtraInfo() {
                            first_foreground_time, started_in_foreground_,
                            user_initiated_info_, url(), start_url_, did_commit_,
                            page_end_reason_, page_end_user_initiated_info_,
-                           page_end_time, metadata_);
+                           page_end_time, metadata_, child_frame_metadata_);
 }
 
 bool PageLoadTracker::HasMatchingNavigationRequestID(