Merge "Short circuit the gainmap shader if we would not apply the gainmap" into main

#ifdef __ANDROID__

static constexpr char gGainmapSKSL[] = R"SKSL(

    uniform shader linearBase;

    uniform shader base;

    uniform shader gainmap;

    uniform colorFilter workingSpaceToLinearSrgb;

    }

    half4 main(float2 coord) {

        half4 S = base.eval(coord);

        if (W == 0.0) {

            return base.eval(coord);

        }

        half4 S = linearBase.eval(coord);

        half4 G = gainmap.eval(coord);

        if (gainmapIsAlpha == 1) {

            G = half4(G.a, G.a, G.a, 1.0);

                SkColorFilterPriv::MakeColorSpaceXform(baseColorSpace, gainmapMathColorSpace);

        // The base image shader will convert into the color space in which the gainmap is applied.

        auto baseImageShader = baseImage->makeRawShader(tileModeX, tileModeY, samplingOptions)

        auto linearBaseImageShader = baseImage->makeRawShader(tileModeX, tileModeY, samplingOptions)

                                             ->makeWithColorFilter(colorXformSdrToGainmap);

        auto baseImageShader = baseImage->makeShader(tileModeX, tileModeY, samplingOptions);

        // The gainmap image shader will ignore any color space that the gainmap has.

        const SkMatrix gainmapRectToDstRect =

                SkMatrix::RectToRect(SkRect::MakeWH(gainmapImage->width(), gainmapImage->height()),

        auto colorXformGainmapToDst = SkColorFilterPriv::MakeColorSpaceXform(

                gainmapMathColorSpace, SkColorSpace::MakeSRGBLinear());

        mBuilder.child("linearBase") = std::move(linearBaseImageShader);

        mBuilder.child("base") = std::move(baseImageShader);

        mBuilder.child("gainmap") = std::move(gainmapImageShader);

        mBuilder.child("workingSpaceToLinearSrgb") = std::move(colorXformGainmapToDst);