cc: Add threaded GPU rasterization.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index dbe343d08446b986f33a688e4b3b0c2c5a251508..db377c556d59debe79e178de54d97fde482cb34d 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -1136,11 +1136,14 @@ float PictureLayerImpl::MaximumTilingContentsScale() const {
 scoped_ptr<PictureLayerTilingSet>
 PictureLayerImpl::CreatePictureLayerTilingSet() {
   const LayerTreeSettings& settings = layer_tree_impl()->settings();
+  float skewport_scaling = 1.0f;
+  if (layer_tree_impl()->use_gpu_rasterization()) {
+    skewport_scaling =
+        settings.threaded_gpu_rasterization_enabled ? 0.2f : 0.0f;

[enne (OOO), 2015/02/11 18:19:51]

Maybe if threaded_gpu_rasterization_enabled, the embedder should just change
skewport_target_time_in_seconds, and then just set this to 0 if
!gpu_rasterization?  That way we can keep these skewports somewhat more
independent.  I don't feel strongly about this, so feel free to ignore.

[vmpstr, 2015/02/11 19:00:51]

I agree, I think this could be nicer if the setting changed when the flag
changes (if it's a command line flag, then it should just determine what
skewport target time at that time as well).

[vmiura, 2015/02/11 20:13:18]

Because of vetoing we want to be able to switch from
(threaded_gpu_rasterization, skewport = 0.2 seconds) to (software_rasterization,
skewport = 1.0 seconds).

So if we code the skewport to 0.2 in RenderWidgetCompositor then that's not
good.

Is there a better place we should do this, or perhaps I should add a separate
settings.gpu_skewport_target_time_in_seconds?

[enne (OOO), 2015/02/11 20:45:15]

Yeah, a different setting seems better, in that case.

(Aren't we getting rid of vetoing?)

[vmiura, 2015/02/11 22:12:50]

Done.
We should, but not ready to go all-in just yet :).

+  }
   return PictureLayerTilingSet::Create(
       this, settings.max_tiles_for_interest_area,
-      layer_tree_impl()->use_gpu_rasterization()
-          ? 0.f
-          : settings.skewport_target_time_in_seconds,
+      settings.skewport_target_time_in_seconds * skewport_scaling,
       settings.skewport_extrapolation_limit_in_content_pixels);
 }