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

chrome/common/localized_error.cc

Index: chrome/common/localized_error.cc
diff --git a/chrome/common/localized_error.cc b/chrome/common/localized_error.cc
index 568b7806a0b89b4cd0ec4f29cfe9e093e5a68a18..3089c7c829eb3ac04d2a6f6585f2e7f8d1ff098f 100644
--- a/chrome/common/localized_error.cc
+++ b/chrome/common/localized_error.cc
@@ -898,15 +898,18 @@ void LocalizedError::EnableGoogleCachedCopyButtonExperiment(
 
       scoped_ptr<base::DictionaryValue> cache_button(new base::DictionaryValue);
 
+      // Google cache copy button label experiment.
       if (field_trial_exp_type_ == kCachedCopyButtonExpTypeCopy) {
         cache_button->SetString(
             "msg",
             l10n_util::GetStringUTF16(IDS_ERRORPAGES_BUTTON_SHOW_CACHED_COPY));
+        cache_button->SetBoolean("defaultLabel", false);
       } else {
         // Default to "Show cached page" button label.
         cache_button->SetString(
             "msg",
             l10n_util::GetStringUTF16(IDS_ERRORPAGES_BUTTON_SHOW_CACHED_PAGE));
+        cache_button->SetBoolean("defaultLabel", true);
       }
       cache_button->SetString("cacheUrl", cache_url);
       cache_button->SetInteger("trackingId", cache_tracking_id);