First patch for async renderengine.

1. return a std::future object from DrawLayers() instead to make it
asynchronously
2. retire drawFence value from drawLayers() parameter list.

Bug: 180657548
Test: android.hardware.graphics.composer@2.2-vts, libcompositionengine_test, libsurfaceflinger_unittest and
librenderengine_test pass

Change-Id: If63c11762d1cce7b053cc72aaeaed6dd7904877f
diff --git a/libs/renderengine/skia/SkiaRenderEngine.h b/libs/renderengine/skia/SkiaRenderEngine.h
index 7cd9eca..f61653b 100644
--- a/libs/renderengine/skia/SkiaRenderEngine.h
+++ b/libs/renderengine/skia/SkiaRenderEngine.h
@@ -44,14 +44,6 @@
     virtual void deleteTextures(size_t /*count*/, uint32_t const* /*names*/) override{};
     virtual bool isProtected() const override { return false; } // mInProtectedContext; }
     virtual bool supportsProtectedContent() const override { return false; };
-    virtual status_t drawLayers(const DisplaySettings& /*display*/,
-                                const std::vector<const LayerSettings*>& /*layers*/,
-                                const std::shared_ptr<ExternalTexture>& /*buffer*/,
-                                const bool /*useFramebufferCache*/,
-                                base::unique_fd&& /*bufferFence*/,
-                                base::unique_fd* /*drawFence*/) override {
-        return 0;
-    };
     virtual int getContextPriority() override { return 0; }
     virtual void assertShadersCompiled(int numShaders) {}
     virtual int reportShadersCompiled() { return 0; }
@@ -60,6 +52,14 @@
     virtual void mapExternalTextureBuffer(const sp<GraphicBuffer>& /*buffer*/,
                                           bool /*isRenderable*/) override = 0;
     virtual void unmapExternalTextureBuffer(const sp<GraphicBuffer>& /*buffer*/) override = 0;
+
+    virtual void drawLayersInternal(
+            const std::shared_ptr<std::promise<RenderEngineResult>>&& resultPromise,
+            const DisplaySettings& display, const std::vector<const LayerSettings*>& layers,
+            const std::shared_ptr<ExternalTexture>& buffer, const bool useFramebufferCache,
+            base::unique_fd&& bufferFence) override {
+        resultPromise->set_value({NO_ERROR, base::unique_fd()});
+    };
 };
 
 } // namespace skia