[cc] Move root layer pointer to LayerTreeImpl

cc/layer_tree_impl.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/layer_tree_impl.h"
+
+#include "cc/layer_tree_host_common.h"
+#include "cc/layer_tree_host_impl.h"
+
+namespace cc {
+
+LayerTreeImpl::LayerTreeImpl(LayerTreeImplClient* client)
+    : client_(client)
+    , source_frame_number_(-1)
+    , hud_layer_(0)
+    , root_scroll_layer_(0)
+    , currently_scrolling_layer_(0)
+    , scrolling_layer_id_from_previous_tree_(0) {
+}
+
+static LayerImpl* findRootScrollLayer(LayerImpl* layer)
+{
+    if (!layer)
+        return 0;
+
+    if (layer->scrollable())
+        return layer;
+
+    for (size_t i = 0; i < layer->children().size(); ++i) {
+        LayerImpl* found = findRootScrollLayer(layer->children()[i]);
+        if (found)
+            return found;
+    }
+
+    return 0;
+}
+
+void LayerTreeImpl::SetRootLayer(scoped_ptr<LayerImpl> layer) {
+  root_layer_ = layer.Pass();
+  root_scroll_layer_ = findRootScrollLayer(root_layer_.get());
+  currently_scrolling_layer_ = 0;
+
+  if (root_layer_ && scrolling_layer_id_from_previous_tree_) {
+    currently_scrolling_layer_ = LayerTreeHostCommon::findLayerInSubtree(
+        root_layer_.get(),
+        scrolling_layer_id_from_previous_tree_);
+  }
+
+  scrolling_layer_id_from_previous_tree_ = 0;
+
+  client_->OnCanDrawStateChangedForTree(this);
+}
+
+scoped_ptr<LayerImpl> LayerTreeImpl::DetachLayerTree() {
+  // Clear all data structures that have direct references to the layer tree.
+  scrolling_layer_id_from_previous_tree_ =
+    currently_scrolling_layer_ ? currently_scrolling_layer_->id() : 0;
+  currently_scrolling_layer_ = 0;
+
+  return root_layer_.Pass();
+}
+
+} // namespace cc