Add UMA histograms for Google cached copy experiment on network error interstitial

chrome/common/localized_error.h

Index: chrome/common/localized_error.h
diff --git a/chrome/common/localized_error.h b/chrome/common/localized_error.h
index ae6ab2a9d8ceb49da6c226b8c3ad636572d2c4a9..bd6e1a9118e55b71adebbc18d3b17de805710eff 100644
--- a/chrome/common/localized_error.h
+++ b/chrome/common/localized_error.h
@@ -51,7 +51,8 @@ class LocalizedError {
  private:
   // Sets up the Google Cached Copy button experiment if part of the
   // field trial. This promotes the Google cached copy suggestion from under
-  // the details section to a blue button.
+  // the details section to a blue button. Also experiments with the
+  // button label.
   static void EnableGoogleCachedCopyButtonExperiment(
       base::ListValue* suggestions,
       base::DictionaryValue* error_strings);