[BlinkGenPropertyTrees] Do not emit UpdateLayers::BuildPropertyTrees

This patch removes UpdateLayers::BuildPropertyTrees trace events when in
layer lists mode which is used by blink gen property trees and slimming
paint v2. This patch also cleans up LayerTreeHost::DoUpdateLayers by
removing the unused in_update_property_trees_ variable.

Bug: 836886

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux-blink-gen-property-trees;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I35e6bd7c59b0384d8c2c62a1d3bdb1eed152353b
Reviewed-on: https://chromium-review.googlesource.com/1176357Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583448}

cc/trees/layer_tree_host.cc

@@ -738,30 +738,28 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
   gfx::Transform identity_transform;
   LayerList update_layer_list;
 
-  {
-    base::AutoReset<bool> update_property_trees(&in_update_property_trees_,
-                                                true);
+  // The non-layer-list mode is used when blink provides cc with a layer tree
+  // and cc needs to compute property trees from that.
+  // In layer lists mode, blink sends cc property trees directly so they do not
+  // need to be built here. Layer lists mode is used by BlinkGenPropertyTrees
+  // and SlimmingPaintV2.
+  if (!IsUsingLayerLists()) {
     TRACE_EVENT0("cc", "LayerTreeHost::UpdateLayers::BuildPropertyTrees");
     TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug.cdp-perf"),
                  "LayerTreeHostCommon::ComputeVisibleRectsWithPropertyTrees");
-    PropertyTrees* property_trees = &property_trees_;
-    if (!IsUsingLayerLists()) {
-      // In SPv2 the property trees should have been built by the
-      // client already.
-      PropertyTreeBuilder::BuildPropertyTrees(
-          root_layer, page_scale_layer, inner_viewport_scroll_layer(),
-          outer_viewport_scroll_layer(), overscroll_elasticity_layer(),
-          elastic_overscroll_, page_scale_factor_, device_scale_factor_,
-          gfx::Rect(device_viewport_size_), identity_transform, property_trees);
-      TRACE_EVENT_INSTANT1("cc",
-                           "LayerTreeHost::UpdateLayers_BuiltPropertyTrees",
-                           TRACE_EVENT_SCOPE_THREAD, "property_trees",
-                           property_trees->AsTracedValue());
+    PropertyTreeBuilder::BuildPropertyTrees(
+        root_layer, page_scale_layer, inner_viewport_scroll_layer(),
+        outer_viewport_scroll_layer(), overscroll_elasticity_layer(),
+        elastic_overscroll_, page_scale_factor_, device_scale_factor_,
+        gfx::Rect(device_viewport_size_), identity_transform, &property_trees_);
+    TRACE_EVENT_INSTANT1("cc", "LayerTreeHost::UpdateLayers_BuiltPropertyTrees",
+                         TRACE_EVENT_SCOPE_THREAD, "property_trees",
+                         property_trees_.AsTracedValue());
     } else {
       TRACE_EVENT_INSTANT1("cc",
                            "LayerTreeHost::UpdateLayers_ReceivedPropertyTrees",
                            TRACE_EVENT_SCOPE_THREAD, "property_trees",
-                           property_trees->AsTracedValue());
+                           property_trees_.AsTracedValue());
     }
 
 #if DCHECK_IS_ON()
@@ -779,8 +777,8 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
     }
 #endif
 
-    draw_property_utils::UpdatePropertyTrees(this, property_trees);
-    draw_property_utils::FindLayersThatNeedUpdates(this, property_trees,
+    draw_property_utils::UpdatePropertyTrees(this, &property_trees_);
+    draw_property_utils::FindLayersThatNeedUpdates(this, &property_trees_,
                                                    &update_layer_list);
 
     // Dump property trees useful for debugging --blink-gen-property-trees
@@ -789,7 +787,7 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
       VLOG(3) << "CC Property Trees:";
       std::string out;
       base::JSONWriter::WriteWithOptions(
-          *property_trees->AsTracedValue()->ToBaseValue(),
+          *property_trees_.AsTracedValue()->ToBaseValue(),
           base::JSONWriter::OPTIONS_PRETTY_PRINT, &out);
       std::stringstream ss(out);
       while (!ss.eof()) {
@@ -798,7 +796,6 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
         VLOG(3) << line;
       }
     }
-  }
 
   bool painted_content_has_slow_paths = false;
   bool painted_content_has_non_aa_paint = false;

cc/trees/layer_tree_host.h

@@ -382,7 +382,6 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   void UnregisterLayer(Layer* layer);
   Layer* LayerById(int id) const;
 
-  bool in_update_property_trees() const { return in_update_property_trees_; }
   bool PaintContent(const LayerList& update_layer_list,
                     bool* content_has_slow_paths,
                     bool* content_has_non_aa_paint);
@@ -701,7 +700,6 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   std::unordered_map<ElementId, Layer*, ElementIdHash> element_layers_map_;
 
   bool in_paint_layer_contents_ = false;
-  bool in_update_property_trees_ = false;
 
   // This is true if atleast one layer in the layer tree has a copy request. We
   // use this bool to decide whether we need to compute subtree has copy request