Introduce a field trial for Instant.

chrome/browser/autocomplete/autocomplete.cc

Index: chrome/browser/autocomplete/autocomplete.cc
diff --git a/chrome/browser/autocomplete/autocomplete.cc b/chrome/browser/autocomplete/autocomplete.cc
index 48e7dd65caa0d29e68a62ef6f280df94d18f94e8..6a87b839bd3047cacac29e08ba73a21b281314ea 100644
--- a/chrome/browser/autocomplete/autocomplete.cc
+++ b/chrome/browser/autocomplete/autocomplete.cc
@@ -25,6 +25,7 @@
 #include "chrome/browser/autocomplete/shortcuts_provider.h"
 #include "chrome/browser/bookmarks/bookmark_model.h"
 #include "chrome/browser/external_protocol/external_protocol_handler.h"
+#include "chrome/browser/instant/instant_field_trial.h"
 #include "chrome/browser/net/url_fixer_upper.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
@@ -793,7 +794,8 @@ AutocompleteController::AutocompleteController(
     AutocompleteControllerDelegate* delegate)
     : delegate_(delegate),
       done_(true),
-      in_start_(false) {
+      in_start_(false),
+      profile_(profile) {
   search_provider_ = new SearchProvider(this, profile);
   providers_.push_back(search_provider_);
   // TODO(mrossetti): Remove the following and permanently modify the
@@ -839,6 +841,7 @@ void AutocompleteController::SetProfile(Profile* profile) {
     (*i)->SetProfile(profile);
   input_.Clear();  // Ensure we don't try to do a "minimal_changes" query on a
                    // different profile.
+  profile_ = profile;
 }
 
 void AutocompleteController::Start(
@@ -880,7 +883,9 @@ void AutocompleteController::Start(
   if (matches_requested == AutocompleteInput::ALL_MATCHES &&
       (text.length() < 6)) {
     base::TimeTicks end_time = base::TimeTicks::Now();
-    std::string name = "Omnibox.QueryTime." + base::IntToString(text.length());
+    std::string name = "Omnibox.QueryTime." +
+                       InstantFieldTrial::GetGroupName(profile_) +
+                       base::IntToString(text.length());

[jar (doing other things), 2011/07/22 01:42:17]

I'm not fully clear on the value of distinguishing based on text.length.  How is
that data helpful?

[sreeram, 2011/07/22 14:31:16]

I am not sure, but that's something that exists currently; I'm just adding the
field trial identifier to it.

     base::Histogram* counter = base::Histogram::FactoryGet(
         name, 1, 1000, 50, base::Histogram::kUmaTargetedHistogramFlag);

[jar (doing other things), 2011/07/22 01:42:17]

You probably want a much larger dynamic range than 1000ms.  I'd suggest
something more like at least 30 seconds, maybe 10 minutes.  You won't lose much
resolution at the low end... but you'll get to see the tail of the distribution.

[sreeram, 2011/07/22 14:31:16]

I think 1s is enough. This is a measure of the responsiveness of the omnibox, so
anything larger than a few tens of milliseconds would already be considered very
bad, so the 1s bucket already captures the tail of the distribution.

     counter->Add(static_cast<int>((end_time - start_time).InMilliseconds()));