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

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 ed8eb0cb5dfa3f118e642f12e997f1776fff7be9..5a165050350a07c25e0a75c59b476c9c196db901 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -825,28 +825,39 @@ void RenderWidget::DoDeferredUpdateAndSendInputAck() {
     Send(pending_input_event_ack_.release());
 }
 
-void RenderWidget::DoDeferredUpdate() {
-  TRACE_EVENT0("renderer", "RenderWidget::DoDeferredUpdate");
-
-  if (!webwidget_)
-    return;
-
+bool RenderWidget::CanDoDeferredUpdate() const {
+  if (!webwidget_) {
+    TRACE_EVENT0("renderer", "EarlyOut_NoWebWidget");
+    return false;
+  }
   if (!host_window_set_) {
     TRACE_EVENT0("renderer", "EarlyOut_NoHostWindow");
-    return;
+    return false;
   }
   if (update_reply_pending_) {
     TRACE_EVENT0("renderer", "EarlyOut_UpdateReplyPending");
-    return;
+    return false;
   }
   if (is_accelerated_compositing_active_ &&
       num_swapbuffers_complete_pending_ >= kMaxSwapBuffersPending) {
     TRACE_EVENT0("renderer", "EarlyOut_MaxSwapBuffersPending");
-    return;
+    return false;
   }
+  return true;
+}
+
+bool RenderWidget::ShouldSuppressDeferredUpdates() const {
+  return is_hidden_ || size_.IsEmpty();
+}
+
+void RenderWidget::DoDeferredUpdate() {
+  TRACE_EVENT0("renderer", "RenderWidget::DoDeferredUpdate");
+
+  if (!CanDoDeferredUpdate())
+    return;
 
   // Suppress updating when we are hidden.
-  if (is_hidden_ || size_.IsEmpty()) {
+  if (ShouldSuppressDeferredUpdates()) {
     paint_aggregator_.ClearPendingUpdate();
     needs_repainting_on_restore_ = true;
     TRACE_EVENT0("renderer", "EarlyOut_NotVisible");
@@ -1184,9 +1195,18 @@ void RenderWidget::didCompleteSwapBuffers() {
   next_paint_flags_ = 0;
 }
 
-void RenderWidget::scheduleComposite() {
+#if defined(WEBWIDGETCLIENT_SCHEDULECOMPOSITE_RETURNS_BOOL)
+#define SC_RETURN_TYPE bool
+#else
+#define SC_RETURN_TYPE void
+#endif
+
+SC_RETURN_TYPE RenderWidget::scheduleComposite() {
   if (WebWidgetHandlesCompositorScheduling()) {
     webwidget_->composite(false);
+#if defined(WEBWIDGETCLIENT_SCHEDULECOMPOSITE_RETURNS_BOOL)
+    return true;
+#endif
   } else {
     // TODO(nduca): replace with something a little less hacky.  The reason this
     // hack is still used is because the Invalidate-DoDeferredUpdate loop
@@ -1195,6 +1215,9 @@ void RenderWidget::scheduleComposite() {
     // duplicating all that code is less desirable than "faking out" the
     // invalidation path using a magical damage rect.
     didInvalidateRect(WebRect(0, 0, 1, 1));
+#if defined(WEBWIDGETCLIENT_SCHEDULECOMPOSITE_RETURNS_BOOL)
+    return CanDoDeferredUpdate() && !ShouldSuppressDeferredUpdates();

[jamesr, 2012/05/08 23:42:40]

what happens if ShouldSuppress...() is false, but when the DoDeferredUpdate
actually runs ShouldSuppress..() has become true (and stays that way)? how do we
make sure that WebKit knows about this state transition?

+#endif
   }
 }