Plugin Power Saver: Add UI Overlay to throttled plugin using placeholder.

content/renderer/pepper/pepper_plugin_instance_impl.cc

Index: content/renderer/pepper/pepper_plugin_instance_impl.cc
diff --git a/content/renderer/pepper/pepper_plugin_instance_impl.cc b/content/renderer/pepper/pepper_plugin_instance_impl.cc
index 768922ec459976eb4f1750f30bbfdd1f66fbd7c0..f8ff874610f67e3479e196a563bbac121fb44c4d 100644
--- a/content/renderer/pepper/pepper_plugin_instance_impl.cc
+++ b/content/renderer/pepper/pepper_plugin_instance_impl.cc
@@ -2043,6 +2043,14 @@ void PepperPluginInstanceImpl::OnThrottleStateChange() {
   SendDidChangeView();
 }
 
+void PepperPluginInstanceImpl::OnHiddenForPlaceholder(bool hidden) {
+  if (hidden) {

[piman, 2015/02/05 00:34:36]

thinking about this a little more, you also need to keep this as a state, and
prevent UpdateLayer when it's set.
Otherwise what could happen is that the plugin is set as hidden because of the
placeholder, but then it decides for any reason to bind a new Graphics2D (or
3D), which will then call UpdateLayer and reattach to the tree.
I think you just need to keep a hidden_for_placeholder_ flag, and early exit in
UpdateLayer if it's set.

[tommycli, 2015/02/05 00:46:35]

Done. I put this flag in the throttler, since dmichael told me to try to
minimize additions to PepperPluginInstanceImpl. Let me know if this is fine.

+    container_->setWebLayer(nullptr);
+  } else {
+    UpdateLayer(true /* device_changed */);
+  }
+}
+
 void PepperPluginInstanceImpl::AddLatencyInfo(
     const std::vector<ui::LatencyInfo>& latency_info) {
   if (render_frame_ && render_frame_->GetRenderWidget()) {