Add support for tracking loading behavior of child frames.

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index ba63fd9f6e830ed1cfb9d68dbd1a4b91c6e8bf65..c17e82e38f311363f16317409a654afc114abd60 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -512,7 +512,9 @@ void MetricsWebContentsObserver::OnTimingUpdated(
     const PageLoadMetadata& metadata) {
   // We may receive notifications from frames that have been navigated away
   // from. We simply ignore them.
-  if (render_frame_host != web_contents()->GetMainFrame()) {
+  if (!render_frame_host->GetRenderViewHost() ||
+      render_frame_host->GetRenderViewHost()->GetMainFrame() !=
+          web_contents()->GetMainFrame()) {
     RecordInternalError(ERR_IPC_FROM_WRONG_FRAME);
     return;
   }
@@ -535,6 +537,15 @@ void MetricsWebContentsObserver::OnTimingUpdated(
   if (error)
     return;
 
+  if (render_frame_host->GetParent() != nullptr) {
+    // Child frames may send PageLoadMetadata updates, but not PageLoadTiming
+    // updates.
+    if (!timing.IsEmpty())
+      RecordInternalError(ERR_TIMING_IPC_FROM_SUBFRAME);
+    committed_load_->UpdateChildFrameMetadata(metadata);
+    return;
+  }
+
   if (!committed_load_->UpdateTiming(timing, metadata)) {
     // If the page load tracker cannot update its timing, something is wrong
     // with the IPC (it's from another load, or it's invalid in some other way).