Skip drawing unsupported layers in forced software mode

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 84c43c20b1c3462b342036d0fbbc7311e9249e28..477ef77b2f6dc031b6e37add99cbab9bde2814b4 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -639,8 +639,10 @@ bool LayerTreeHostImpl::CalculateRenderPasses(FrameData* frame) {
               &has_occlusion_from_outside_target_surface)) {
         append_quads_data.had_occlusion_from_outside_target_surface |=
             has_occlusion_from_outside_target_surface;
-      } else {
+      } else if (!output_surface_->ForcedDrawToSoftwareDevice() ||

[aelias_OOO_until_Jul13, 2013/05/29 22:30:47]

Seems like an arbitrary place to bail out... I suggest early-returning in
AppendQuadsForLayer() and AppendQuadsForRenderSurfaceLayer() based on the value
of append_quads_data.allow_tile_draw_quads .  (Alternatively we could exclude
this entire loop contents with a "continue" above occlusion_tracker.EnterLayer,
but I'm thinking the finer-grained early return would be easier to reason
about.)

[boliu, 2013/05/30 00:01:28]

Went with option 2 stead, skip the whole loop body if draw not supported. This
is because WillDraw/DidDraw call pairs might be doing somethings that are kind
of heavy (and possibly not supported?) in this mode. Eg, video layer acquires a
lock, texture layer creates resource, etc. Probably good to skip those as well.

+                 it->CanDrawInTilelessSoftwareMode()) {
         DCHECK_EQ(active_tree_, it->layer_tree_impl());
+
         it->WillDraw(resource_provider_.get());
         frame->will_draw_layers.push_back(*it);