Avoid sending empty OnRepaint msgs and propagate window damage correctly

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index f58b8a069a769ad30b793dc27dbc1e4523bc2e6a..7ebcb81fbc09b92952b4561ba274825399c39650 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -1876,11 +1876,11 @@ void RenderWidget::OnRepaint(const gfx::Size& size_to_paint) {
   if (!webwidget_)
     return;
 
+  DCHECK(!size_to_paint.IsEmpty());

[jamesr, 2013/04/16 22:21:56]

I'm hitting this on several mac tests:

[13367:263:0416/145747:FATAL:render_widget.cc(1879)] Check failed:
!size_to_paint.IsEmpty().

will try to figure out where it's coming from and if it's a problem before
landing

+
   set_next_paint_is_repaint_ack();
-  if (is_accelerated_compositing_active_) {
-    if (compositor_)
-      compositor_->setNeedsRedraw();
-    scheduleComposite();
+  if (is_accelerated_compositing_active_ && compositor_) {
+    compositor_->SetNeedsRedrawRect(gfx::Rect(size_to_paint));

[piman, 2013/04/16 22:04:05]

I'm curious - I thought setNeedsRedraw would force a paint on the whole
viewport, which ought to be a superset of what we pass to SetNeedsRedrawRect.
I guess you're saying, in the case where RW was resized to (0,0) but RWH doesn't
know that yet, we still need to produce a frame - and this would force it to
happen, but I wonder if someone starts thinking that we should clip the redraw
rect to the viewport (not unreasonable), this would break.
Should we add a (pre-emptive) cc test that verifies that SetNeedsRedrawRect
really does generate a frame even when the viewport is empty?

   } else {
     gfx::Rect repaint_rect(size_to_paint.width(), size_to_paint.height());
     didInvalidateRect(repaint_rect);