Remove dependency from SignInBrowsertest on tracing events watching

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
index 2516925aca9ae7e0e81c00db4ef1f9db33316843..50d6c646d2631b354f60126337c93a07db943a86 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -113,6 +113,9 @@ const int kMaxGaiaReloadForProxyAuthDialog = 3;
 const char kSourceGaiaSignin[] = "gaia-signin";
 const char kSourceAccountPicker[] = "account-picker";
 
+base::LazyInstance<base::Closure> g_ui_shown_callback_for_testing_ =
+    LAZY_INSTANCE_INITIALIZER;

[stevenjb, 2016/10/14 17:31:55]

No trailing _ in file local variables.

If this is just a Closure*, we don't need to use LazyInstance:

base::Closure* g_ui_shown_callback_for_testing = nullptr;

Then below:

if (g_ui_shown_callback_for_testing)
  g_ui_shown_callback_for_testing->Run();

[Primiano Tucci (use gerrit), 2016/10/14 17:42:56]

I am not sure I follow, how do you expect the g_closure ptr to be set?
Definitely It cannot be set to a pointer to some stack allocated thing.
The only alternative way I see is doing
g_closure = new base::Closure ....

but this will make memory sanitizers unhappy because will be seen as a leak.
At this point you could add a ANNOTATE_LEAKING_OBJECT_PTR, but at this point you
now have more complexity than lazyinstance itself.

+
 static bool Contains(const std::vector<std::string>& container,
                      const std::string& value) {
   return std::find(container.begin(), container.end(), value) !=
@@ -364,6 +367,13 @@ void SigninScreenHandler::SetUserInputMethod(
   }
 }
 
+// static
+void SigninScreenHandler::SetCallbackOnUiShownForTesting(
+    base::Closure callback) {
+  DCHECK(g_ui_shown_callback_for_testing_.Get().is_null());
+  g_ui_shown_callback_for_testing_.Get() = callback;
+}
+
 void SigninScreenHandler::DeclareLocalizedValues(
     ::login::LocalizedValuesBuilder* builder) {
   // Format numbers to be used on the pin keyboard.
@@ -1256,6 +1266,8 @@ void SigninScreenHandler::HandleLoginVisible(const std::string& source) {
         content::NotificationService::NoDetails());
     TRACE_EVENT_ASYNC_END0(
         "ui", "ShowLoginWebUI", LoginDisplayHostImpl::kShowLoginWebUIid);
+    if (!g_ui_shown_callback_for_testing_.Get().is_null())
+      g_ui_shown_callback_for_testing_.Get().Run();
   }
   webui_visible_ = true;
   if (preferences_changed_delayed_)