Restrict Instant field trial to UMA opt-in users.

chrome/browser/autocomplete/autocomplete.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/autocomplete/autocomplete.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
@@ skipping 866 matching lines @@
   for (ACProviders::iterator i(providers_.begin()); i != providers_.end();
        ++i) {
     (*i)->Start(input_, minimal_changes);
     if (matches_requested != AutocompleteInput::ALL_MATCHES)
       DCHECK((*i)->done());
   }
   if (matches_requested == AutocompleteInput::ALL_MATCHES &&
       (text.length() < 6)) {
     base::TimeTicks end_time = base::TimeTicks::Now();
     std::string name = "Omnibox.QueryTime." +
-                       InstantFieldTrial::GetGroupName(profile_) +
+                       InstantFieldTrial::GetGroupName(profile_) + "." +
                        base::IntToString(text.length());
     base::Histogram* counter = base::Histogram::FactoryGet(
         name, 1, 1000, 50, base::Histogram::kUmaTargetedHistogramFlag);
     counter->Add(static_cast<int>((end_time - start_time).InMilliseconds()));
   }
   in_start_ = false;
   CheckIfDone();
   UpdateResult(true);
 
   if (!done_)
@@ skipping 135 matching lines @@
     }
   }
   done_ = true;
 }
 
 void AutocompleteController::StartExpireTimer() {
   if (result_.HasCopiedMatches())
     expire_timer_.Start(base::TimeDelta::FromMilliseconds(kExpireTimeMS),
                         this, &AutocompleteController::ExpireCopiedEntries);
 }