PlzNavigate: fix crash when updating redirect timing.

third_party/WebKit/Source/web/WebDataSourceImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 59 matching lines @@
     return DocumentLoader::unreachableURL();
 }
 
 void WebDataSourceImpl::appendRedirect(const WebURL& url)
 {
     DocumentLoader::appendRedirect(url);
 }
 
 void WebDataSourceImpl::updateNavigation(double redirectStartTime, double redirectEndTime, double fetchStartTime, const WebVector<WebURL>& redirectChain)
 {
-    for (size_t i = 0; i + 1 < redirectChain.size(); ++i)
-        didRedirect(redirectChain[i], redirectChain[i + 1]);
-    timing().setRedirectStart(redirectStartTime);
-    timing().setRedirectEnd(redirectEndTime);
+    if (redirectChain.size() >= 2) {

[Nate Chapin, 2016/09/30 23:03:57]

Please add a comment to explain the significance of 2 here.

+        for (size_t i = 0; i + 1 < redirectChain.size(); ++i)
+            didRedirect(redirectChain[i], redirectChain[i + 1]);
+        timing().setRedirectStart(redirectStartTime);
+        timing().setRedirectEnd(redirectEndTime);
+    }
     timing().setFetchStart(fetchStartTime);
 }
 
 void WebDataSourceImpl::redirectChain(WebVector<WebURL>& result) const
 {
     result.assign(m_redirectChain);
 }
 
 bool WebDataSourceImpl::isClientRedirect() const
 {
@@ skipping 69 matching lines @@
 {
     DocumentLoader::setSubresourceFilter(WTF::wrapUnique(subresourceFilter));
 }
 
 DEFINE_TRACE(WebDataSourceImpl)
 {
     DocumentLoader::trace(visitor);
 }
 
 } // namespace blink