RenderWidget's scheduleComposite should return a bool. (true iff a prompt composite will come).

content/renderer/render_widget.cc

 // Copyright (c) 2012 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 "content/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 1143 matching lines @@
   params.view_size = size_;
   params.plugin_window_moves.swap(plugin_window_moves_);
   params.flags = next_paint_flags_;
   params.scroll_offset = GetScrollOffset();
   params.needs_ack = false;
 
   Send(new ViewHostMsg_UpdateRect(routing_id_, params));
   next_paint_flags_ = 0;
 }
 
+#if defined(WEBWIDGETCLIENT_SCHEDULECOMPOSITE_RETURNS_BOOL)
+bool RenderWidget::scheduleComposite() {

[nduca, 2012/05/02 06:53:00]

Can you fix this with less code duplication? E.g.
#if returnsbool
#define sc_return_value bool
#else
#define sc_return_value void
#endif

then inside the function, #if sc_returns_bool
custom return
#endif

+  if (WebWidgetHandlesCompositorScheduling()) {
+    webwidget_->composite(false);
+    return true;
+  }
+
+  // TODO(nduca): replace with something a little less hacky.  The reason this
+  // hack is still used is because the Invalidate-DoDeferredUpdate loop
+  // contains a lot of host-renderer synchronization logic that is still
+  // important for the accelerated compositing case. The option of simply
+  // duplicating all that code is less desirable than "faking out" the
+  // invalidation path using a magical damage rect.
+  didInvalidateRect(WebRect(0, 0, 1, 1));
+  return !is_hidden_;

[nduca, 2012/05/02 06:53:00]

This feels fragile to me. You're assuming things here about didInvalidateRect.
It woul dbe better for didInvalidateRect to give the return value. Do this by
moving the body of didInval to a DoInvalidateRect function and then making
didInvalidateRect just call to Do?

+}
+#else
 void RenderWidget::scheduleComposite() {
   if (WebWidgetHandlesCompositorScheduling()) {
     webwidget_->composite(false);
   } else {
     // TODO(nduca): replace with something a little less hacky.  The reason this
     // hack is still used is because the Invalidate-DoDeferredUpdate loop
     // contains a lot of host-renderer synchronization logic that is still
     // important for the accelerated compositing case. The option of simply
     // duplicating all that code is less desirable than "faking out" the
     // invalidation path using a magical damage rect.
     didInvalidateRect(WebRect(0, 0, 1, 1));
   }
 }
+#endif
 
 void RenderWidget::scheduleAnimation() {
   if (animation_update_pending_)
     return;
 
   TRACE_EVENT0("gpu", "RenderWidget::scheduleAnimation");
   animation_update_pending_ = true;
   if (!animation_timer_.IsRunning()) {
     animation_timer_.Start(FROM_HERE, base::TimeDelta::FromSeconds(0), this,
                            &RenderWidget::AnimationCallback);
@@ skipping 509 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }