cc: Re-enable GPU rasterization after content veto.

cc/trees/layer_tree_host.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 757 matching lines @@
     root_layer_->SetLayerTreeHost(this);
   }
 
   if (hud_layer_.get())
     hud_layer_->RemoveFromParent();
 
   // Reset gpu rasterization flag.
   // 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();
 }
 
 void LayerTreeHost::SetDebugState(const LayerTreeDebugState& debug_state) {
   LayerTreeDebugState new_debug_state =
       LayerTreeDebugState::Unite(settings_.initial_debug_state, debug_state);
 
   if (LayerTreeDebugState::Equal(debug_state_, new_debug_state))
     return;
@@ skipping 255 matching lines @@
     draw_property_utils::FindLayersThatNeedUpdates(
         this, property_trees_.transform_tree, property_trees_.effect_tree,
         &update_layer_list);
   }
 
   for (const auto& layer : update_layer_list)
     layer->SavePaintProperties();
 
   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;
 }
 
 void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
   for (auto& swap_promise : info->swap_promises) {
     TRACE_EVENT_WITH_FLOW1("input,benchmark",
                            "LatencyInfo.Flow",
                            TRACE_ID_DONT_MANGLE(swap_promise->TraceId()),
                            TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT,
                            "step", "Main thread scroll update");
@@ skipping 694 matching lines @@
   int seq_num = property_trees_.sequence_number;
   LayerTreeHostCommon::CallFunctionForEveryLayer(this, [seq_num](Layer* layer) {
     layer->set_property_tree_sequence_number(seq_num);
   });
 
   surface_id_namespace_ = proto.surface_id_namespace();
   next_surface_sequence_ = proto.next_surface_sequence();
 }
 
 }  // namespace cc