Prevent recreation of UI resource holder when created with resource ID

cc/layers/ui_resource_layer.cc

Index: cc/layers/ui_resource_layer.cc
diff --git a/cc/layers/ui_resource_layer.cc b/cc/layers/ui_resource_layer.cc
index 944cf7d54844c7016feb32eacfc401fb590146ab..02783325b9fffcfd126f8151deea38c02592e315 100644
--- a/cc/layers/ui_resource_layer.cc
+++ b/cc/layers/ui_resource_layer.cc
@@ -25,6 +25,8 @@ class ScopedUIResourceHolder : public UIResourceLayer::UIResourceHolder {
   }
   UIResourceId id() override { return resource_->id(); }
 
+  bool NeedsRecreation() override { return false; }
+
  private:
   ScopedUIResourceHolder(LayerTreeHost* host, const SkBitmap& skbitmap) {
     resource_ = ScopedUIResource::Create(host, UIResourceBitmap(skbitmap));
@@ -41,6 +43,8 @@ class SharedUIResourceHolder : public UIResourceLayer::UIResourceHolder {
 
   UIResourceId id() override { return id_; }
 
+  bool NeedsRecreation() override { return true; }
+
  private:
   explicit SharedUIResourceHolder(UIResourceId id) : id_(id) {}
 
@@ -112,10 +116,11 @@ void UIResourceLayer::SetLayerTreeHost(LayerTreeHost* host) {
 }
 
 void UIResourceLayer::RecreateUIResourceHolder() {
-  ui_resource_holder_ = nullptr;
   if (layer_tree_host() && !bitmap_.empty()) {
     ui_resource_holder_ =
         ScopedUIResourceHolder::Create(layer_tree_host(), bitmap_);
+  } else if (ui_resource_holder_ && !ui_resource_holder_->NeedsRecreation()) {

[danakj, 2014/10/31 14:23:35]

So when you attach a layer to a LayerTreeHost its resource ID namespace becomes
that of the LTH.

Does it make sense to call UIResourceLayer::SetUIResourceId() when it's not
attached to a LayerTreeHost? Why does this need to be done? Without a LTH it has
no namespace for that uiresourceid.

[Changwan Ryu, 2014/11/06 00:27:27]

Hmm.. Let me give you more background:

Because we aren't in control of the timing of when SetLayerTreeHost would be
called, we simply do not know when to set UI resource ID.

Previously, we did this by overriding SetLayerTreeHost in an inheriting class,
but we are trying to switching from inheritance to containment model. (See the
bug for more details.)

If UI resource ID should be tied to a resource namespace (which is specific to
LTH), probably what we should do is try to get some callback when
SetLayerTreeHost is called. Do you have any suggestion of where we can do it?

+    ui_resource_holder_ = nullptr;
   }
   UpdateDrawsContent(HasDrawableContent());
 }