cc: Let skia veto gpu rasterization.

cc/layers/picture_layer.cc

Index: cc/layers/picture_layer.cc
diff --git a/cc/layers/picture_layer.cc b/cc/layers/picture_layer.cc
index dee9a78bc950e185644ed90e3b3bdb17fd6538c5..5827af27eb531a722bdafe51755c40674dbf16e2 100644
--- a/cc/layers/picture_layer.cc
+++ b/cc/layers/picture_layer.cc
@@ -20,7 +20,7 @@ PictureLayer::PictureLayer(ContentLayerClient* client)
       pile_(make_scoped_refptr(new PicturePile())),
       instrumentation_object_tracker_(id()),
       is_mask_(false),
-      has_gpu_rasterization_hint_(false),
+      has_gpu_rasterization_hint_(TRIBOOL_UNKNOWN),
       update_source_frame_number_(-1) {}
 
 PictureLayer::~PictureLayer() {
@@ -50,7 +50,7 @@ void PictureLayer::PushPropertiesTo(LayerImpl* base_layer) {
   }
 
   layer_impl->SetIsMask(is_mask_);
-  layer_impl->SetHasGpuRasterizationHint(has_gpu_rasterization_hint_);
+  layer_impl->SetUseGpuRasterization(ShouldUseGpuRasterization());
 
   // Unlike other properties, invalidation must always be set on layer_impl.
   // See PictureLayerImpl::PushPropertiesTo for more details.
@@ -138,11 +138,34 @@ void PictureLayer::SetIsMask(bool is_mask) {
 }
 
 void PictureLayer::SetHasGpuRasterizationHint(bool has_hint) {
-  DCHECK(IsPropertyChangeAllowed());
-  if (has_gpu_rasterization_hint_ == has_hint)
-    return;
-  has_gpu_rasterization_hint_ = has_hint;
-  SetNeedsCommit();
+  switch (has_gpu_rasterization_hint_) {
+    case TRIBOOL_UNKNOWN:  // Fall-through.
+    case TRIBOOL_TRUE:
+      has_gpu_rasterization_hint_ = has_hint ? TRIBOOL_TRUE : TRIBOOL_FALSE;
+      break;
+    case TRIBOOL_FALSE:
+      // GPU rasterization cannot be enabled once disabled.
+      // This is done to prevent frequent invalidations and visual flashing.
+      break;
+    default:
+      NOTREACHED();
+  }
+  // No need to commit immediately.
+  // This flag will be pushed with the next commit.

[enne (OOO), 2014/04/04 18:34:19]

I'm confused why the SetNeedsCommit went away.

[alokp, 2014/04/04 18:50:34]

If only the hint changes and the layer is still valid, there is no need to do
anything immediately. If there is an invalidation (current or future) we will
re-raster everything so that it is consistent across the layer. I will add more
comments if this sounds reasonable to you.

[enne (OOO), 2014/04/04 19:40:07]

Yeah, this just seems a little dodgy to me, because it seems like you should at
least be setting "needs push properties".  I guess you could argue that if
there's any invalidation then properties will need to be pushed, so this will
get covered, but it's subtle.

A comment would help a lot, since normally most code sets a property and then
sets needs commit / needs push properties, so it looks missing.

+}
+
+bool PictureLayer::ShouldUseGpuRasterization() const {
+  switch (layer_tree_host()->settings().rasterization_site) {
+    case LayerTreeSettings::CpuRasterization:
+      return false;
+    case LayerTreeSettings::HybridRasterization:
+      return has_gpu_rasterization_hint_ == TRIBOOL_TRUE &&
+             pile_->is_suitable_for_gpu_rasterization();
+    case LayerTreeSettings::GpuRasterization:
+      return true;
+  }
+  NOTREACHED();
+  return false;
 }
 
 bool PictureLayer::SupportsLCDText() const {