Chromium M34上图像（IMG元素）的直接合成，不走NativeImageSkia::draw路径的相关代码

// An image can be directly compositing if it's the sole content of the layer, and has no box decorations
// that require painting. Direct compositing saves backing store.
bool CompositedLayerMapping::isDirectlyCompositedImage() const
{
    RenderObject* renderObject = renderer();

    if (!renderObject->isImage() || m_owningLayer->hasBoxDecorationsOrBackground() || renderObject->hasClip())
        return false;

    RenderImage* imageRenderer = toRenderImage(renderObject);
    if (ImageResource* cachedImage = imageRenderer->cachedImage()) {
        if (!cachedImage->hasImage())
            return false;

        Image* image = cachedImage->imageForRenderer(imageRenderer);
        return image->isBitmapImage();
    }

    return false;
}// An image can be directly compositing if it's