Restrict Instant field trial to UMA opt-in users.

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 6a87b839bd3047cacac29e08ba73a21b281314ea..4b8ac92e27aa5c3cc323424a0b1347dc357abed6 100644
--- a/chrome/browser/autocomplete/autocomplete.cc
+++ b/chrome/browser/autocomplete/autocomplete.cc
@@ -884,7 +884,7 @@ void AutocompleteController::Start(
       (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);