Refactor screen/monitor so that gfx::Screen returns monitor object.

ui/gfx/monitor.cc

+// Copyright (c) 2012 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 "ui/gfx/monitor.h"
+
+namespace gfx {
+
+Monitor::Monitor() {
+}
+
+Monitor::~Monitor() {
+}
+
+Size Monitor::GetSize() const {
+  return GetBounds().size();
+}
+
+Size Monitor::GetWorkAreaSize() const {
+  return GetWorkArea().size();
+}
+
+SimpleMonitor::SimpleMonitor()
+    : bounds_(gfx::Rect(0, 0, 1, 1)),
+      work_area_(bounds_) {
+}
+
+SimpleMonitor::SimpleMonitor(const gfx::Rect& bounds)
+    : bounds_(bounds),
+      work_area_(bounds) {
+}
+
+SimpleMonitor::~SimpleMonitor() {
+}
+
+Rect SimpleMonitor::GetBounds() const {
+  return bounds_;
+}
+
+Rect SimpleMonitor::GetWorkArea() const {
+  return work_area_;
+}
+
+float SimpleMonitor::GetDeviceScaleFactor() const {
+  return 1.0;
+}
+
+}  // namespace gfx