Add UMA metrics for profile switching.

chrome/browser/ui/webui/signin/user_manager_screen_handler.cc

Index: chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
diff --git a/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc b/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
index 91a5bce179edad88405345fd32f252e11d843bb6..9e40230d7c7132b7cb342404b8d9b93a29fdc7cc 100644
--- a/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
+++ b/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
@@ -386,7 +386,6 @@ void UserManagerScreenHandler::HandleRemoveUser(const base::ListValue* args) {
 
 void UserManagerScreenHandler::HandleLaunchGuest(const base::ListValue* args) {
   if (IsGuestModeEnabled()) {
-    ProfileMetrics::LogProfileSwitchUser(ProfileMetrics::SWITCH_PROFILE_GUEST);

[Mike Lerman, 2015/01/21 20:58:03]

Why did you remove this? It's definitely interesting to know how often the Guest
Profile was opened.

[anthonyvd, 2015/01/21 21:12:18]

We ended up logging it twice.  Once here and once in
profiles::SwitchToGuestProfile so I removed it here and all code paths that go
through SwitchToGuestProfile log it.

     profiles::SwitchToGuestProfile(
         desktop_type_,
         base::Bind(&UserManagerScreenHandler::OnSwitchToProfileComplete,