Remove NOTREACHED that gets hit for non well formed xhtml.

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/page_load_metrics/metrics_web_contents_observer.h"
 
 #include <algorithm>
 #include <ostream>
 #include <string>
 #include <utility>
@@ skipping 138 matching lines @@
     return false;
   }
 
   if (!EventsInOrder(timing.dom_loading, timing.first_layout)) {
     NOTREACHED() << "Invalid dom_loading " << timing.dom_loading
                  << " for first_layout " << timing.first_layout;
     return false;
   }
 
   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;
   }
 
   if (!EventsInOrder(timing.first_paint, timing.first_text_paint)) {
     NOTREACHED() << "Invalid first_paint " << timing.first_paint
                  << " for first_text_paint " << timing.first_text_paint;
     return false;
   }
 
   if (!EventsInOrder(timing.first_paint, timing.first_image_paint)) {
@@ skipping 781 matching lines @@
     if (navigation_handle->IsSamePage() || navigation_handle->IsErrorPage())
       return false;
     const std::string& mime_type = web_contents()->GetContentsMimeType();
     if (mime_type != "text/html" && mime_type != "application/xhtml+xml")
       return false;
   }
   return true;
 }
 
 }  // namespace page_load_metrics