linux: fix windowless Flash when scrolling

chrome/plugin/webplugin_proxy.cc

Index: chrome/plugin/webplugin_proxy.cc
diff --git a/chrome/plugin/webplugin_proxy.cc b/chrome/plugin/webplugin_proxy.cc
index 6aee64561f1c391a623fde987b7be23c719efd92..0e2e006f47760656b78ad1734fcc6e62b08ca8d0 100644
--- a/chrome/plugin/webplugin_proxy.cc
+++ b/chrome/plugin/webplugin_proxy.cc
@@ -182,6 +182,12 @@ void WebPluginProxy::InvalidateRect(const gfx::Rect& rect) {
   // Ignore NPN_InvalidateRect calls with empty rects.  Also don't send an
   // invalidate if it's outside the clipping region, since if we did it won't
   // lead to a paint and we'll be stuck waiting forever for a DidPaint response.
+  //
+  // TODO(piman): There is a race condition here, because this test assumes
+  // that when the paint actually occurs, the clip rect will not have changed.
+  // This is not true because scrolling (or window resize) could occur and be
+  // handled by the renderer before it receives the InvalidateRect message,
+  // changing the clip rect and then not painting.
   if (rect.IsEmpty() || !delegate_->GetClipRect().Intersects(rect))
     return;