Remove NOTREACHED that gets hit for non well formed xhtml.

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 4f1635151f42b52ef3e52a75ff967db51a72ba94..b8b781541f2b0d7d2a956496400dc1c665ab3671 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -156,8 +156,10 @@ bool IsValidPageLoadTiming(const PageLoadTiming& timing) {
   }
 
   if (!EventsInOrder(timing.first_layout, timing.first_paint)) {
-    NOTREACHED() << "Invalid first_layout " << timing.first_layout
-                 << " for first_paint " << timing.first_paint;
+    // This can happen when we process an XHTML document that doesn't contain
+    // well formed XML. See crbug.com/627607.
+    DLOG(ERROR) << "Invalid first_layout " << timing.first_layout
+                << " for first_paint " << timing.first_paint;
     return false;
   }