Add support for multiple roots to the client lib.

mojo/services/public/cpp/view_manager/lib/view_manager_private.cc

Index: mojo/services/public/cpp/view_manager/lib/view_manager_private.cc
diff --git a/mojo/services/public/cpp/view_manager/lib/view_manager_private.cc b/mojo/services/public/cpp/view_manager/lib/view_manager_private.cc
index e350f3426dfd42481358e7edf35b12b38c697308..92756dcefa7236bec9b07be1b2a53c1e07d3615f 100644
--- a/mojo/services/public/cpp/view_manager/lib/view_manager_private.cc
+++ b/mojo/services/public/cpp/view_manager/lib/view_manager_private.cc
@@ -4,13 +4,62 @@
 
 #include "mojo/services/public/cpp/view_manager/lib/view_manager_private.h"
 
+#include "mojo/services/public/cpp/view_manager/lib/view_tree_node_private.h"
+#include "mojo/services/public/cpp/view_manager/view_tree_node_observer.h"
+
 namespace mojo {
 namespace view_manager {
+namespace {
+
+// Responsible for removing a root from the ViewManager when that node is
+// destroyed.
+class RootObserver : public ViewTreeNodeObserver {
+ public:
+  explicit RootObserver(ViewTreeNode* root) : root_(root) {}
+  virtual ~RootObserver() {}
+
+ private:
+  // Overridden from ViewTreeNodeObserver:
+  virtual void OnNodeDestroy(ViewTreeNode* node,
+                             DispositionChangePhase phase) OVERRIDE {
+    DCHECK_EQ(node, root_);
+    if (phase != ViewTreeNodeObserver::DISPOSITION_CHANGED)
+      return;
+    ViewManagerPrivate(
+        ViewTreeNodePrivate(root_).view_manager()).RemoveRoot(root_);
+  }
+
+  ViewTreeNode* root_;
+
+  DISALLOW_COPY_AND_ASSIGN(RootObserver);
+};
+
+}  // namespace
 
 ViewManagerPrivate::ViewManagerPrivate(ViewManager* manager)
     : manager_(manager) {}
 ViewManagerPrivate::~ViewManagerPrivate() {}
 
+void ViewManagerPrivate::AddRoot(ViewTreeNode* root) {
+  // A new root must not already exist as a root or be contained by an existing
+  // hierarchy visible to this view manager.
+  std::vector<ViewTreeNode*>::const_iterator it = manager_->roots().begin();
+  for (; it != manager_->roots().end(); ++it) {
+    if (*it == root || (*it)->Contains(root))
+      return;
+  }
+  manager_->roots_.push_back(root);
+  root->AddObserver(new RootObserver(root));
+  manager_->root_added_callback_.Run(manager_);
+}
+
+void ViewManagerPrivate::RemoveRoot(ViewTreeNode* root) {
+  std::vector<ViewTreeNode*>::iterator it =
+      std::find(manager_->roots_.begin(), manager_->roots_.end(), root);
+  if (it != manager_->roots_.end())
+    manager_->roots_.erase(it);
+}
+
 void ViewManagerPrivate::AddNode(TransportNodeId node_id, ViewTreeNode* node) {
   DCHECK(!manager_->nodes_[node_id]);
   manager_->nodes_[node_id] = node;