Use Windowing system-specific WindowContext factories.

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
deleted file mode 100644
index 7bb24ba30b6352500b8a683fa25c898c0d398fae..0000000000000000000000000000000000000000
--- a/tools/viewer/sk_app/android/RasterWindowContext_android.h
+++ /dev/null
@@ -1,40 +0,0 @@
-
-/*
- * 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:
-    friend RasterWindowContext* RasterWindowContext::Create(
-            void* platformData, const DisplayParams&);
-
-    sk_sp<SkSurface> getBackbufferSurface() override;
-    void swapBuffers() override;
-
-    bool isValid() override { return SkToBool(fNativeWindow); }
-    void resize(uint32_t w, uint32_t h) override;
-    void setDisplayParams(const DisplayParams& params) override;
-
-private:
-    RasterWindowContext_android(void* platformData, const DisplayParams& params);
-    void setBuffersGeometry();
-    sk_sp<SkSurface> fBackbufferSurface = nullptr;
-    ANativeWindow* fNativeWindow = nullptr;
-    ANativeWindow_Buffer fBuffer;
-    ARect fBounds;
-};
-
-}   // namespace sk_app
-
-#endif