cros: Remove usage of GaiaScreenHandler outside of login/webui.

chrome/browser/chromeos/login/screens/gaia_view.h

Index: chrome/browser/chromeos/login/screens/gaia_view.h
diff --git a/chrome/browser/chromeos/login/screens/gaia_view.h b/chrome/browser/chromeos/login/screens/gaia_view.h
new file mode 100644
index 0000000000000000000000000000000000000000..04af20e95294457c22f804debbd6bc4bd1cb54aa
--- /dev/null
+++ b/chrome/browser/chromeos/login/screens/gaia_view.h
@@ -0,0 +1,33 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_GAIA_VIEW_H_
+#define CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_GAIA_VIEW_H_
+
+#include <string>
+
+#include "base/bind.h"
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+
+namespace chromeos {
+
+class GaiaView {
+ public:
+  GaiaView() = default;
+  virtual ~GaiaView() = default;
+
+  // Decides whether an auth extension should be pre-loaded. If it should,
+  // pre-loads it.
+  virtual void MaybePreloadAuthExtension() = 0;
+
+  virtual void DisableRestrictiveProxyCheckForTest() = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(GaiaView);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_GAIA_VIEW_H_