Bug 92697

RenderObject needs a fast-path for removeAllChildren Looking at the sample of the benchmark attached to bug 92258. We see nearly 10% of total time (on a 300x300 grid sample), spent under ContainerNode::removeChildren() tearing down the associated rendering tree. Each renderer goes through and tell its ancestor chain that it's dying, and marks the view as needing repaint for its rect. We spend a bunch of time computing those repaint rects, and walking up/down the ancestor chain. Just like how we have a "fast path" for removing subtrees in the DOM, we need some smarter logic for removing subtrees in the rendering tree. At least in the non-positioned, flow cases, we should be able to have a single repaint rect instead of all this nonsense.