linux: fix windowless Flash when scrolling

chrome/plugin/webplugin_proxy.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/plugin/webplugin_proxy.h"
 
 #include "build/build_config.h"
 #if defined(OS_LINUX)
 #include <gtk/gtk.h>
 #endif
@@ skipping 164 matching lines @@
                  delegate_->GetRect().width(),
                  delegate_->GetRect().height());
   InvalidateRect(rect);
 }
 
 void WebPluginProxy::InvalidateRect(const gfx::Rect& rect) {
   damaged_rect_ = damaged_rect_.Union(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;
 
   // Only send a single InvalidateRect message at a time.  From DidPaint we
   // will dispatch an additional InvalidateRect message if necessary.
   if (!waiting_for_paint_) {
     waiting_for_paint_ = true;
     // Invalidates caused by calls to NPN_InvalidateRect/NPN_InvalidateRgn
     // need to be painted asynchronously as per the NPAPI spec.
     MessageLoop::current()->PostTask(FROM_HERE,
@@ skipping 481 matching lines @@
   while (index != resource_clients_.end()) {
     WebPluginResourceClient* client = (*index).second;
 
     if (client == resource_client) {
       resource_clients_.erase(index++);
     } else {
       index++;
     }
   }
 }