Skip drawing unsupported layers in forced software mode

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 0bf84806d136fabf32fd49cad7887cc1a195ba3c..5f1fe9ae7a717fe43d069541d393876b726678a4 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -419,6 +419,8 @@ class CC_EXPORT LayerImpl : LayerAnimationValueObserver {
   scoped_ptr<base::Value> AsValue() const;
   virtual size_t GPUMemoryUsageInBytes() const;
 
+  virtual bool CanDrawInTilelessSoftwareMode() const;

[enne (OOO), 2013/05/30 17:04:37]

I am generally averse to yet more virtual boolean pseudo-RTTI functions on
LayerImpl, in part because it creates distance between the flag-checking code,
the code that's avoided, and this flag function itself.

I think I'd prefer making other layer types behave like PictureLayerImpl in that
you ask the layers and they make some decision to behave differently if needed.

What do you think about having WillDraw/AppendQuadsData take an explicit enum of
{ hardware, software, resourceless } and each layer type could do its best to
meet that request? WillDraw could even return a boolean to imply that the layer
can't support that mode.

That would also make testing easier.  You could have all layer types (there's a
test helper for this) crossed with all drawing modes so it'd be clear that all
layer types were safe in all modes.

+
  protected:
   LayerImpl(LayerTreeImpl* layer_impl, int id);