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;

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

In other words, keep this function the same as before...

+      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.
+}
+
+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 &&

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

...and just say has_gpu_rasterization_hint_ &&
pile_->is_suitable_for_gpu_rasterization().

It just seems like you're maintaining redundant state (the "has ever been
disabled" state) in the TRIBOOL and the pile suitability flag.

[alokp, 2014/04/04 21:53:46]

I do not think there is any redundancy. Both the flags - has-hint and
is-suitable - are sticky but controlled by two different independent signals -
will-change and skia-veto.

If I understand your proposal, it may not work if the content is always
gpu-suitable:
1. The default value of has-hint is false, so we raster with cpu.
2. SetHasGpuRasterizationHint(true)
3. Invalidation - contents is gpu-suitable
4. Raster with gpu
5. SetHasGpuRasterizationHint(false)
6. Invalidation - contents still gpu-suitable
7. Raster with cpu
8. SetHasGpuRasterizationHint(true)
9. Invalidation - contents still gpu-suitable
10. Raster with gpu

In short, we can keep switch between cpu and gpu if the content continues to be
gpu-suitable. Please let me know if you had something else in mind.

I have used boost::tribool in the past to represent unknown boolean state and it
seems appropriate in this case. A two-state boolean does not work because the
default state is the same as the sticky state. I can add another bool if it
makes it less confusing.

+             pile_->is_suitable_for_gpu_rasterization();
+    case LayerTreeSettings::GpuRasterization:
+      return true;
+  }
+  NOTREACHED();
+  return false;
 }
 
 bool PictureLayer::SupportsLCDText() const {