Find root scroll layer at tree activation

cc/top_controls_manager_unittest.cc

Index: cc/top_controls_manager_unittest.cc
diff --git a/cc/top_controls_manager_unittest.cc b/cc/top_controls_manager_unittest.cc
index d081042f99404c05904bbdb2b988023f4de5de5d..79274c97755207a78e29c6ee3e60f71fd95e1194 100644
--- a/cc/top_controls_manager_unittest.cc
+++ b/cc/top_controls_manager_unittest.cc
@@ -27,7 +27,6 @@ class MockTopControlsManagerClient : public TopControlsManagerClient {
         update_draw_properties_needed_(false) {
     active_tree_ = LayerTreeImpl::create(&host_impl_);
     root_scroll_layer_ = LayerImpl::create(active_tree_.get(), 1);
-    active_tree_->set_root_scroll_layer(root_scroll_layer_.get());
   }
 
   virtual ~MockTopControlsManagerClient() {}
@@ -40,20 +39,25 @@ class MockTopControlsManagerClient : public TopControlsManagerClient {
     update_draw_properties_needed_ = true;
   }
 
-  virtual LayerTreeImpl* activeTree() OVERRIDE {
-    return active_tree_.get();
+  virtual bool haveRootScrollLayer() const OVERRIDE {
+    return true;
   }
 
-  TopControlsManager* manager() {
-    if (!manager_)
-      manager_ = TopControlsManager::Create(this, kTopControlsHeight);
-    return manager_.get();
+  virtual float rootScrollLayerTotalScrollY() const OVERRIDE {
+    return root_scroll_layer_->scrollOffset().y() +
+           root_scroll_layer_->scrollDelta().y();
   }
 
   LayerImpl* rootScrollLayer() {
     return root_scroll_layer_.get();
   }
 
+  TopControlsManager* manager() {
+    if (!manager_)
+      manager_ = TopControlsManager::Create(this, kTopControlsHeight);
+    return manager_.get();
+  }
+
  private:
   FakeImplProxy proxy_;
   FakeLayerTreeHostImpl host_impl_;