Simplify LayerTreeHost::DoUpdateLayers for layer-list and non-list modes

LayerTreeHost::DoUpdateLayers is responsible for initiating property
tree building in non-layer-list mode, and setting some hud layer state
in layer-list mode. This patch moves list and non-list logic into their
respective conditional blocks.

Layer list mode currently references the root layer for the hud layer
properties. This will likely change in the future, possibly referencing
the first layer instead of the root layer.

With this refactoring it became clear that
HeadsUpDisplayLayer::PrepareForCalculateDrawProperties was no longer a
relevant name so the function was simplified and inlined into
LayerTreeHost::UpdateHudLayer.

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ia1d8a9530e9b9706a70012707c2ba36253e89845
Reviewed-on: https://chromium-review.googlesource.com/1200825
Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588577}

cc/layers/heads_up_display_layer.cc

@@ -8,8 +8,6 @@
 
 #include "base/trace_event/trace_event.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
-#include "cc/trees/layer_tree_host.h"
-#include "cc/trees/layer_tree_settings.h"
 
 namespace cc {
 
@@ -29,28 +27,6 @@ HeadsUpDisplayLayer::HeadsUpDisplayLayer()
 
 HeadsUpDisplayLayer::~HeadsUpDisplayLayer() = default;
 
-void HeadsUpDisplayLayer::PrepareForCalculateDrawProperties(
-    const gfx::Size& device_viewport, float device_scale_factor) {
-  gfx::Size device_viewport_in_layout_pixels = gfx::Size(
-      device_viewport.width() / device_scale_factor,
-      device_viewport.height() / device_scale_factor);
-
-  gfx::Size bounds;
-  gfx::Transform matrix;
-  matrix.MakeIdentity();
-
-  if (layer_tree_host()->GetDebugState().ShowHudRects()) {
-    bounds = device_viewport_in_layout_pixels;
-  } else {
-    int size = 256;
-    bounds.SetSize(size, size);
-    matrix.Translate(device_viewport_in_layout_pixels.width() - size, 0.0);
-  }
-
-  SetBounds(bounds);
-  SetTransform(matrix);
-}
-
 bool HeadsUpDisplayLayer::HasDrawableContent() const {
   return true;
 }

cc/layers/heads_up_display_layer.h

@@ -20,9 +20,6 @@ class CC_EXPORT HeadsUpDisplayLayer : public Layer {
  public:
   static scoped_refptr<HeadsUpDisplayLayer> Create();
 
-  void PrepareForCalculateDrawProperties(
-      const gfx::Size& device_viewport, float device_scale_factor);
-
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
 
   // Layer overrides.

cc/trees/layer_tree_host.cc

@@ -729,30 +729,6 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
 
   UpdateHudLayer(debug_state_.ShowHudInfo());
 
-  Layer* root_scroll =
-      PropertyTreeBuilder::FindFirstScrollableLayer(root_layer);
-  Layer* page_scale_layer = viewport_layers_.page_scale.get();
-  if (!page_scale_layer && root_scroll)
-    page_scale_layer = root_scroll->parent();
-
-  if (hud_layer_) {
-    hud_layer_->PrepareForCalculateDrawProperties(device_viewport_size_,
-                                                  device_scale_factor_);
-    // The HUD layer is managed outside the layer list sent to LayerTreeHost
-    // and needs to have its property tree state set.
-    if (IsUsingLayerLists() && root_layer_.get()) {
-      hud_layer_->SetTransformTreeIndex(root_layer_->transform_tree_index());
-      hud_layer_->SetEffectTreeIndex(root_layer_->effect_tree_index());
-      hud_layer_->SetClipTreeIndex(root_layer_->clip_tree_index());
-      hud_layer_->SetScrollTreeIndex(root_layer_->scroll_tree_index());
-      hud_layer_->set_property_tree_sequence_number(
-          root_layer_->property_tree_sequence_number());
-    }
-  }
-
-  gfx::Transform identity_transform;
-  LayerList update_layer_list;
-
   // 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
@@ -762,6 +738,12 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
     TRACE_EVENT0("cc", "LayerTreeHost::UpdateLayers::BuildPropertyTrees");
     TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug.cdp-perf"),
                  "LayerTreeHostCommon::ComputeVisibleRectsWithPropertyTrees");
+    Layer* root_scroll =
+        PropertyTreeBuilder::FindFirstScrollableLayer(root_layer);
+    Layer* page_scale_layer = viewport_layers_.page_scale.get();
+    if (!page_scale_layer && root_scroll)
+      page_scale_layer = root_scroll->parent();
+    gfx::Transform identity_transform;
     PropertyTreeBuilder::BuildPropertyTrees(
         root_layer, page_scale_layer, inner_viewport_scroll_layer(),
         outer_viewport_scroll_layer(), overscroll_elasticity_element_id(),
@@ -775,6 +757,16 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
                            "LayerTreeHost::UpdateLayers_ReceivedPropertyTrees",
                            TRACE_EVENT_SCOPE_THREAD, "property_trees",
                            property_trees_.AsTracedValue());
+      // The HUD layer is managed outside the layer list sent to LayerTreeHost
+      // and needs to have its property tree state set.
+      if (hud_layer_ && root_layer_.get()) {
+        hud_layer_->SetTransformTreeIndex(root_layer_->transform_tree_index());
+        hud_layer_->SetEffectTreeIndex(root_layer_->effect_tree_index());
+        hud_layer_->SetClipTreeIndex(root_layer_->clip_tree_index());
+        hud_layer_->SetScrollTreeIndex(root_layer_->scroll_tree_index());
+        hud_layer_->set_property_tree_sequence_number(
+            root_layer_->property_tree_sequence_number());
+      }
     }
 
 #if DCHECK_IS_ON()
@@ -793,6 +785,8 @@ bool LayerTreeHost::DoUpdateLayers(Layer* root_layer) {
 #endif
 
     draw_property_utils::UpdatePropertyTrees(this, &property_trees_);
+
+    LayerList update_layer_list;
     draw_property_utils::FindLayersThatNeedUpdates(this, &property_trees_,
                                                    &update_layer_list);
 
@@ -1378,9 +1372,13 @@ void LayerTreeHost::SetElasticOverscrollFromImplSide(
 
 void LayerTreeHost::UpdateHudLayer(bool show_hud_info) {
   if (show_hud_info) {
-    if (!hud_layer_.get()) {
+    if (!hud_layer_.get())
       hud_layer_ = HeadsUpDisplayLayer::Create();
-    }
+
+    gfx::Size device_viewport_in_layout_pixels =
+        gfx::Size(device_viewport_size_.width() / device_scale_factor_,
+                  device_viewport_size_.height() / device_scale_factor_);
+    hud_layer_->SetBounds(device_viewport_in_layout_pixels);
 
     if (root_layer_.get() && !hud_layer_->parent())
       root_layer_->AddChild(hud_layer_);

cc/trees/layer_tree_host.h

@@ -417,6 +417,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   void SetElasticOverscrollFromImplSide(gfx::Vector2dF elastic_overscroll);
   gfx::Vector2dF elastic_overscroll() const { return elastic_overscroll_; }
 
+  // Ensures a HUD layer exists if it is needed, and updates the layer bounds.
+  // If a HUD layer exists but is no longer needed, it is destroyed.
   void UpdateHudLayer(bool show_hud_info);
   HeadsUpDisplayLayer* hud_layer() const { return hud_layer_.get(); }