[page_load_metrics] Add support for chrome:// urls and add extensions observer

chrome/browser/page_load_metrics/metrics_web_contents_observer.h

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.h
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
index d52a54cde7e652f03eede2e91a35f44d1b3a97d1..2f7810eff7813951e92e31368b46f0fc04d75509 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
@@ -73,6 +73,9 @@ enum InternalErrorLoadEvent {
   // was not http/s. This can happen with the renderer sending IPCs for the
   // new tab page. This will often come paired with
   // ERR_IPC_WITH_NO_RELEVANT_LOAD.
+  //
+  // DEPRECATED: our IPC policy is now relaxed to enable logging metrics for
+  // chrome URLs.
   ERR_IPC_FROM_BAD_URL_SCHEME,
 
   // If we track a navigation, but the renderer sends us no IPCs. This could
@@ -230,6 +233,8 @@ class PageLoadTracker {
   // committed load.
   void LogAbortChainHistograms(content::NavigationHandle* final_navigation);
 
+  void FilterObservers(content::NavigationHandle* navigation_handle);
+
   // Whether we stopped tracking this navigation after it was initiated. We may
   // stop tracking a navigation if it doesn't meet the criteria for tracking
   // metrics in DidFinishNavigation.