Add UMA to track app launcher discoverability.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 5724f543245a5615f9c6bea10dd0060944253778..cee68e06b8cde272e56f9a030efec11f7e096a4d 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2548,7 +2548,7 @@ const char kRLZDisabled[] = "rlz.disabled";
 #if defined(ENABLE_APP_LIST)
 // The directory in user data dir that contains the profile to be used with the
 // app launcher.
-extern const char kAppListProfile[] = "app_list.profile";
+const char kAppListProfile[] = "app_list.profile";
 
 // Whether to show the app list on a browser relaunch. Used when switching out
 // of metro mode after a user gesture requests showing the app list.
@@ -2556,18 +2556,25 @@ const char kRestartWithAppList[] = "app_list.show_on_relaunch";
 
 // The number of times the app launcher was launched since last ping and
 // the time of the last ping.
-extern const char kAppListLaunchCount[] = "app_list.launch_count";
-extern const char kLastAppListLaunchPing[] = "app_list.last_launch_ping";
+const char kAppListLaunchCount[] = "app_list.launch_count";
+const char kLastAppListLaunchPing[] = "app_list.last_launch_ping";
 
 // The number of times the an app was launched from the app launcher since last
 // ping and the time of the last ping.
-extern const char kAppListAppLaunchCount[] = "app_list.app_launch_count";
-extern const char kLastAppListAppLaunchPing[] = "app_list.last_app_launch_ping";
+const char kAppListAppLaunchCount[] = "app_list.app_launch_count";
+const char kLastAppListAppLaunchPing[] = "app_list.last_app_launch_ping";
 
 // A boolean that tracks whether the user has ever enabled the app launcher.
 const char kAppLauncherHasBeenEnabled[] =
     "apps.app_launcher.has_been_enabled";
 
+// An enum indicating how the app launcher was enabled. E.g., via webstore, app
+// install, command line, etc. For UMA.
+const char kAppListEnableMethod[] = "app_list.how_enabled";
+
+// The time that the app launcher was enabled. Cleared when UMA is recorded.
+const char kAppListEnableTime[] = "app_list.when_enabled";
+
 // TODO(calamity): remove this pref since app launcher will always be
 // installed.
 // Local state caching knowledge of whether the app launcher is installed.