Use the new hotword extension in the launcher when it is enabled.

chrome/browser/search/hotword_service.cc

Index: chrome/browser/search/hotword_service.cc
diff --git a/chrome/browser/search/hotword_service.cc b/chrome/browser/search/hotword_service.cc
index e29a08ff4fa424dd9e944fc2a24f96fd567e1172..2f75b0394f5b73731f80cbde6ea0afd001deb541 100644
--- a/chrome/browser/search/hotword_service.cc
+++ b/chrome/browser/search/hotword_service.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/search/hotword_service.h"
 
+#include "base/command_line.h"
 #include "base/i18n/case_conversion.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
@@ -20,6 +21,7 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search/hotword_service_factory.h"
 #include "chrome/common/chrome_paths.h"
+#include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/extension_constants.h"
 #include "chrome/common/pref_names.h"
 #include "content/public/browser/browser_thread.h"
@@ -173,6 +175,12 @@ bool HotwordService::DoesHotwordSupportLanguage(Profile* profile) {
   return false;
 }
 
+// static
+bool HotwordService::IsExperimentalHotwordingEnabled() {
+  CommandLine* command_line = CommandLine::ForCurrentProcess();
+  return command_line->HasSwitch(switches::kEnableExperimentalHotwording);
+}
+
 HotwordService::HotwordService(Profile* profile)
     : profile_(profile),
       extension_registry_observer_(this),
@@ -447,7 +455,7 @@ void HotwordService::OnHotwordSearchEnabledChanged(
 }
 
 void HotwordService::RequestHotwordSession(HotwordClient* client) {
-  if (!IsServiceAvailable() || client_)
+  if (!IsServiceAvailable() || (client_ && client_ != client))
     return;
 
   client_ = client;