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

components/error_page/common/net_error_info.h

 // Copyright (c) 2013 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.
 
 #ifndef COMPONENTS_ERROR_PAGE_COMMON_NET_ERROR_INFO_H_
 #define COMPONENTS_ERROR_PAGE_COMMON_NET_ERROR_INFO_H_
 
 // TODO(hashimoto): Change this to namespace error_page.
 namespace chrome_common_net {
 
@@ skipping 15 matching lines @@
 
   NETWORK_ERROR_PAGE_BROWSER_INITIATED_RELOAD,   // Reload from browser.
 
   // Keep track of which button the user chooses when both are shown.
   NETWORK_ERROR_PAGE_BOTH_BUTTONS_SHOWN,
   NETWORK_ERROR_PAGE_BOTH_BUTTONS_RELOAD_CLICKED,
   NETWORK_ERROR_PAGE_BOTH_BUTTONS_SHOWN_SAVED_COPY_CLICKED,
 
   NETWORK_ERROR_EASTER_EGG_ACTIVATED,            // Easter egg activated.
 
+  // For "Google cached copy" button.
+  NETWORK_ERROR_PAGE_CACHED_COPY_BUTTON_SHOWN,
+  NETWORK_ERROR_PAGE_CACHED_COPY_BUTTON_CLICKED,
+  NETWORK_ERROR_PAGE_CACHED_PAGE_BUTTON_SHOWN,
+  NETWORK_ERROR_PAGE_CACHED_PAGE_BUTTON_CLICKED,

[mmenke, 2015/07/20 18:14:27]

Is the only difference here the label?  I don't think that's at all clear from
the code here, in net_error_helper_core.h, or in localized_error.cc.

Suggest some comment making it clearer.  Maybe 'For "Google cached copy"
button.' -> 'For "Google cached copy" button label experiment.'  Suggest doing
something similar at the other locations.

[mmenke, 2015/07/20 18:14:27]

These are presumably going to be removed at some point.  To avoid making the
histogram a weird mix of old and new values, that gives us two options:

1)  Add numbers to the events, and when events are removed, comment out the old
values, so new histograms won't re-use the values.
2)  Rename the histogram whenever we change it.  This has the upside of not
mixing data from the two different histograms.  Not as important here, as this
is more of an event count than an actual histogram, but does make sure we're
comparing comparable values.

[edwardjung, 2015/07/21 11:43:37]

Makes sense. Added comments.

[edwardjung, 2015/07/21 11:43:37]

Yes these would be removed once the experiment would be over. I'll implement
option 1 for now. 

+
   NETWORK_ERROR_PAGE_EVENT_MAX,
 };
 
 // The status of a DNS probe.
 //
 // The DNS_PROBE_FINISHED_* values are used in histograms, so:
 // 1. FINISHED_UNKNOWN must remain the first FINISHED_* value.
 // 2. FINISHED_* values must not be rearranged relative to FINISHED_UNKNOWN.
 // 3. New FINISHED_* values must be inserted at the end.
 // 4. New non-FINISHED_* values cannot be inserted.
@@ skipping 45 matching lines @@
 // Record specific error page events.
 void RecordEvent(NetworkErrorPageEvent event);
 
 // The error domain used to pass DNS probe statuses to the localized error
 // code.
 extern const char kDnsProbeErrorDomain[];
 
 }  // namespace chrome_common_net
 
 #endif  // COMPONENTS_ERROR_PAGE_COMMON_NET_ERROR_INFO_H_