Update toast behavior and apperance according to UX requirement

chrome/browser/android/vr_shell/ui_elements/exclusive_screen_toast.cc

+// 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.
+
+#include "chrome/browser/android/vr_shell/ui_elements/exclusive_screen_toast.h"
+
+#include "chrome/browser/android/vr_shell/textures/ui_texture.h"
+#include "chrome/browser/android/vr_shell/ui_elements/textured_element.h"
+
+namespace vr_shell {
+
+ExclusiveScreenToast::ExclusiveScreenToast(int preferred_width)
+    : SimpleTexturedElement(preferred_width) {}
+
+ExclusiveScreenToast::~ExclusiveScreenToast() = default;
+
+void ExclusiveScreenToast::UpdateElementSize() {
+  // Adjust the width of this element according to the texture. The width is
+  // decided by the length of the text to show.
+  gfx::SizeF drawn_size = GetTexture()->GetDrawnSize();
+  float width = drawn_size.width() / drawn_size.height() * size().y();
+  set_size({width, size().y(), 1});
+}
+
+}  // namespace vr_shell