[WebRTC] Implement Windows ScreenDrawer to test ScreenCapturer*

webrtc/modules/desktop_capture/screen_drawer.h

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef MODULES_DESKTOP_CAPTURE_SCREEN_DRAWER_H_
+#define MODULES_DESKTOP_CAPTURE_SCREEN_DRAWER_H_
+
+#include <stdint.h>
+
+#include <memory>
+
+#include "webrtc/modules/desktop_capture/desktop_geometry.h"
+
+namespace webrtc {
+
+// A set of platform independent functions to draw various of shapes on the
+// screen. This class is for testing ScreenCapturer* implementations only, and
+// should not be used in production logic.
+class ScreenDrawer {
+ public:
+  // Creates a ScreenDrawer for the current platform.
+  static std::unique_ptr<ScreenDrawer> Create();
+
+  ScreenDrawer() {}
+  virtual ~ScreenDrawer() {}
+
+  // Returns a rect, on which this instance can draw.
+  virtual DesktopRect DrawableRegion() = 0;
+
+  // Draws a rectangle to cover |rect| with color |rgba|. Note, rect.bottom()
+  // and rect.right() two lines are not included.
+  virtual void DrawRectangle(DesktopRect rect, uint32_t rgba) = 0;
+
+  // Clears all content on the screen. Each platform can have its specific
+  // implementation, but a default one is to draw a white rectangle on entire
+  // DrawableRegion().
+  virtual void Clear();
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_DESKTOP_CAPTURE_SCREEN_DRAWER_H_