cc: Make sure we don't insert or remove layers during painting

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 918d5db58fc8c1d738e4e025f2985a9b896f10b9..5969a16006af73f915831d609d272abda2523012 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -118,6 +118,7 @@ LayerTreeHost::LayerTreeHost(InitParams* params)
       shared_bitmap_manager_(params->shared_bitmap_manager),
       gpu_memory_buffer_manager_(params->gpu_memory_buffer_manager),
       task_graph_runner_(params->task_graph_runner),
+      in_update_(false),
       surface_id_namespace_(0u),
       next_surface_sequence_(1u) {
   DCHECK(task_graph_runner_);
@@ -796,6 +797,7 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
   for (const auto& layer : update_layer_list)
     layer->SavePaintProperties();
 
+  in_update_ = true;
   base::AutoReset<bool> painting(&in_paint_layer_contents_, true);
   bool did_paint_content = false;
   for (const auto& layer : update_layer_list) {
@@ -806,6 +808,7 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
     content_is_suitable_for_gpu_rasterization_ &=
         layer->IsSuitableForGpuRasterization();
   }
+  in_update_ = false;
   return did_paint_content;
 }