Prerender: Remove deprecated prerender experiment histograms.

chrome/browser/prerender/prerender_histograms.cc

Index: chrome/browser/prerender/prerender_histograms.cc
diff --git a/chrome/browser/prerender/prerender_histograms.cc b/chrome/browser/prerender/prerender_histograms.cc
index 9df289dd32d738337524938e56c2e93133175a6e..3e4b4bfa1915016af5bb4cf47d24037264b2f2f0 100644
--- a/chrome/browser/prerender/prerender_histograms.cc
+++ b/chrome/browser/prerender/prerender_histograms.cc
@@ -153,8 +153,7 @@ void PrerenderHistograms::RecordPrerender(Origin origin, const GURL& url) {
 void PrerenderHistograms::RecordPrerenderStarted(Origin origin) const {
   if (OriginIsOmnibox(origin)) {
     UMA_HISTOGRAM_ENUMERATION(
-        base::StringPrintf("Prerender.OmniboxPrerenderCount%s",
-                           PrerenderManager::GetModeString()), 1, 2);
+        "Prerender.OmniboxPrerenderCount", 1, 2);

[pasko, 2016/08/24 13:08:29]

this histogram (Prerender.OmniboxNavigationsUsedPrerenderCount_Enabled) and
another one below are actually recorded and query-able in the dashboard, just
marked as unowned and obsolete, hence not discoverable.

Please update the histograms.xml to say that the _Enabled thing is deprecated.
The thing without the suffix is now becoming owned, yay, no modifications
required.

We have not looked at them before, but let's keep, may be useful.

[mattcary, 2016/08/24 15:49:11]

Ah, thanks. My uma-foo is weak, I didn't realize that something could exist but
not be discoverable.

However, there doesn't seem to be any OmniboxPrerenderCount_Enabled in
histograms.xml, or any reference to PrerenderMode from OmniboxPrerenderCount. So
I don't think there's any further deprecation do be done.

In other words, all this CL will do is stop producing the old_* metrics in favor
of simpler names (that are already attached to owners).

[pasko, 2016/08/24 17:51:37]

the fact that *_Enabled is not in histograms.xml is a bug, smb did not update it
carefully, I wanted to correct it with one small change.

On the other hand, these suffixes are messed up and not reflecting what's
recorded, and it was this way in 2012 already. Feel free to ignore this
suggestion.


I think this would be good to fix here, however:

* let's announce _all_ of the <histogram_suffixes name="Prerender"> as obsolete,
they are incorrect, but as this change lands they'd become even more puzzling.

* <histogram_suffixes name="PrerenderSource"> contain these incorrect suffixes
as affected-histogram, let's obsolete them too. Example:

<affected-histogram name="Prerender.FinalStatus_Prerender5minTTL"/>

   }
 }
 
@@ -170,8 +169,7 @@ void PrerenderHistograms::RecordConcurrency(size_t prerender_count) const {
 void PrerenderHistograms::RecordUsedPrerender(Origin origin) const {
   if (OriginIsOmnibox(origin)) {
     UMA_HISTOGRAM_ENUMERATION(
-        base::StringPrintf("Prerender.OmniboxNavigationsUsedPrerenderCount%s",
-                           PrerenderManager::GetModeString()), 1, 2);
+        "Prerender.OmniboxNavigationsUsedPrerenderCount", 1, 2);
   }
 }