minui: Move graphics_{adf,drm,fbdev} into classes.

This CL defines minui_backend as an interface, and expresses the three
backends (adf, drm and fbdev) as subclasses to the interface.

Test: 'Run graphics test' on N9, Pixel C and N5X.
Change-Id: I0e23951c7b2e2ff918957a8d9fc8b0085b6e5952
diff --git a/minui/graphics_fbdev.h b/minui/graphics_fbdev.h
new file mode 100644
index 0000000..107e195
--- /dev/null
+++ b/minui/graphics_fbdev.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _GRAPHICS_FBDEV_H_
+#define _GRAPHICS_FBDEV_H_
+
+#include <linux/fb.h>
+
+#include "graphics.h"
+#include "minui/minui.h"
+
+class MinuiBackendFbdev : public MinuiBackend {
+ public:
+  GRSurface* Init() override;
+  GRSurface* Flip() override;
+  void Blank(bool) override;
+  ~MinuiBackendFbdev() override;
+  MinuiBackendFbdev();
+
+ private:
+  void SetDisplayedFramebuffer(unsigned n);
+
+  GRSurface gr_framebuffer[2];
+  bool double_buffered;
+  GRSurface* gr_draw;
+  int displayed_buffer;
+  fb_var_screeninfo vi;
+  int fb_fd;
+};
+
+#endif  // _GRAPHICS_FBDEV_H_