Add error description to the DidFailProvisionalLoad callback.

content/renderer/mock_content_renderer_client.cc

Index: content/renderer/mock_content_renderer_client.cc
diff --git a/content/renderer/mock_content_renderer_client.cc b/content/renderer/mock_content_renderer_client.cc
index b8a8e6de758b0c717e1ae2d1d758f643906794f1..65ceb65917a2a1538b54b3bc94374e24642d22dd 100644
--- a/content/renderer/mock_content_renderer_client.cc
+++ b/content/renderer/mock_content_renderer_client.cc
@@ -48,6 +48,12 @@ std::string MockContentRendererClient::GetNavigationErrorHtml(
   return std::string();
 }
 
+string16 MockContentRendererClient::GetNavigationErrorDescription(
+    const WebKit::WebURLRequest& failed_request,
+    const WebKit::WebURLError& error) {
+  return string16();
+}
+
 bool MockContentRendererClient::RunIdleHandlerWhenWidgetsHidden() {
   return true;
 }