cc: Re-enable GPU rasterization after content veto.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 903236ec060f00df4cf06b52e4188581bda9c359..c68e9f525224e135f45fb0191ea672f5d028652d 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -775,6 +775,7 @@ void LayerTreeHost::SetRootLayer(scoped_refptr<Layer> root_layer) {
   // This flag is sticky until a new tree comes along.
   content_is_suitable_for_gpu_rasterization_ = true;
   gpu_rasterization_histogram_recorded_ = false;
+  num_times_gpu_rasterization_reenabled_ = 0;
 
   SetNeedsFullTreeSync();
 }
@@ -1050,11 +1051,23 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
 
   base::AutoReset<bool> painting(&in_paint_layer_contents_, true);
   bool did_paint_content = false;
+  bool old_content_is_suitable_for_gpu_rasterization =
+      content_is_suitable_for_gpu_rasterization_;
+  // Every |kFramePeriodToReeanbleGpuRasterization|, try to re-enable GPU
+  // raserization. Only do this if we haven't re-enabled it too many times.
+  if ((source_frame_number_ % kFramePeriodToReeanbleGpuRasterization) == 0 &&

[enne (OOO), 2016/06/30 01:02:24]

I think it might be safer to say "if the last N frames have been ok, then
reenable" vs just unflipping and peeking at the new value again every N frames.

+      num_times_gpu_rasterization_reenabled_ <
+          kMaxTimesToEnableGpuRasterization) {
+    content_is_suitable_for_gpu_rasterization_ = true;

[ericrk, 2016/06/30 18:46:00]

Can we always set this to true? Or do we want to check if the content is
suitable at this point?

+  }
   for (const auto& layer : update_layer_list) {
     did_paint_content |= layer->Update();
     content_is_suitable_for_gpu_rasterization_ &=
         layer->IsSuitableForGpuRasterization();
   }
+  num_times_gpu_rasterization_reenabled_ +=
+      !old_content_is_suitable_for_gpu_rasterization &&
+      content_is_suitable_for_gpu_rasterization_;
   return did_paint_content;
 }