WIP - compositor worker mega patch.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 3519f293b6256ada4302075487c1362c8fd818da..3bf1907450e74ed94c57329dbdfd40133423dd69 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -45,6 +45,15 @@
 
 namespace cc {
 
+namespace {
+
+const uint32_t kMainLayerFlags =
+    LayerTreeMutation::MUTATION_OPACITY | LayerTreeMutation::MUTATION_TRANSFORM;
+const uint32_t kScrollLayerFlags = LayerTreeMutation::MUTATION_SCROLL_LEFT |
+                                   LayerTreeMutation::MUTATION_SCROLL_TOP;
+
+}  // namespace
+
 LayerTreeImpl::LayerTreeImpl(
     LayerTreeHostImpl* layer_tree_host_impl,
     scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
@@ -359,6 +368,46 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
   target_tree->has_ever_been_drawn_ = false;
 }
 
+void LayerTreeImpl::AddToElementMap(LayerImpl* layer) {
+  TRACE_EVENT2("compositor-worker", "LayerTreeImpl::AddToElementMap",
+               "element_id", layer->element_id(), "layer_id", layer->id());
+  ElementLayers& layers = element_layers_map_[layer->element_id()];
+  if (layer->mutable_properties() & kMainLayerFlags) {
+    if (!layers.main || layer->IsActive())
+      layers.main = layer;
+  }
+  if (layer->mutable_properties() & kScrollLayerFlags) {
+    if (!layers.scroll || layer->IsActive()) {
+      TRACE_EVENT2("compositor-worker", "LayerTreeImpl::AddToElementMap scroll",
+                   "element_id", layer->element_id(), "layer_id", layer->id());
+      layers.scroll = layer;
+    }
+  }
+}
+
+void LayerTreeImpl::RemoveFromElementMap(LayerImpl* layer) {
+  TRACE_EVENT2("compositor-worker", "LayerTreeImpl::RemoveFromElementMap",
+               "element_id", layer->element_id(), "layer_id", layer->id());
+  ElementLayers& layers = element_layers_map_[layer->element_id()];
+  if (layer->mutable_properties() & kMainLayerFlags)
+    layers.main = nullptr;
+  if (layer->mutable_properties() & kScrollLayerFlags)
+    layers.scroll = nullptr;
+
+  if (!layers.main && !layers.scroll)
+    element_layers_map_.erase(layer->element_id());
+}
+
+bool LayerTreeImpl::GetMutableLayers(uint64_t element_id,
+                                     ElementLayers* element_layers) {
+  auto iter = element_layers_map_.find(element_id);
+  if (iter == element_layers_map_.end())
+    return false;
+
+  *element_layers = iter->second;
+  return true;
+}
+
 LayerImpl* LayerTreeImpl::InnerViewportContainerLayer() const {
   return InnerViewportScrollLayer()
              ? InnerViewportScrollLayer()->scroll_clip_layer()