Implement Raster Backend on Android Viewer App

tools/viewer/sk_app/android/RasterWindowContext_android.h

Index: tools/viewer/sk_app/android/RasterWindowContext_android.h
diff --git a/tools/viewer/sk_app/android/RasterWindowContext_android.h b/tools/viewer/sk_app/android/RasterWindowContext_android.h
new file mode 100644
index 0000000000000000000000000000000000000000..b9dc9527aa3368b66a7fc4c598f9c062892e1384
--- /dev/null
+++ b/tools/viewer/sk_app/android/RasterWindowContext_android.h
@@ -0,0 +1,30 @@
+
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef RasterWindowContext_android_DEFINED
+#define RasterWindowContext_android_DEFINED
+
+#include <android/native_window_jni.h>
+
+#include "../RasterWindowContext.h"
+
+namespace sk_app {
+
+class RasterWindowContext_android : public RasterWindowContext {
+public:
+    RasterWindowContext_android(void* platformData, const DisplayParams& params);
+
+protected:
+    void onSwapBuffers(sk_sp<SkImage>) override;
+
+private:
+    ANativeWindow* fNativeWindow = nullptr;
+};
+
+}   // namespace sk_app
+
+#endif