Reify view ownership as a message pipe.

services/ui/view_manager/view_tree_state.cc

Index: services/ui/view_manager/view_tree_state.cc
diff --git a/services/ui/view_manager/view_tree_state.cc b/services/ui/view_manager/view_tree_state.cc
index 4a69f2c318d7815e7c64c36b37269ce9c66826d3..1d8f502cf45081349aac27e268985347d05f178d 100644
--- a/services/ui/view_manager/view_tree_state.cc
+++ b/services/ui/view_manager/view_tree_state.cc
@@ -4,41 +4,56 @@
 
 #include "services/ui/view_manager/view_tree_state.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
+#include "services/ui/view_manager/view_registry.h"
+#include "services/ui/view_manager/view_state.h"
+#include "services/ui/view_manager/view_stub.h"
+#include "services/ui/view_manager/view_tree_host_impl.h"
 
 namespace view_manager {
 
-ViewTreeState::ViewTreeState(mojo::ui::ViewTreePtr view_tree,
-                             mojo::ui::ViewTreeTokenPtr view_tree_token,
-                             const std::string& label)
+ViewTreeState::ViewTreeState(
+    ViewRegistry* registry,
+    mojo::ui::ViewTreePtr view_tree,
+    mojo::ui::ViewTreeTokenPtr view_tree_token,
+    mojo::InterfaceRequest<mojo::ui::ViewTreeHost> view_tree_host_request,
+    const std::string& label)
     : view_tree_(view_tree.Pass()),
       view_tree_token_(view_tree_token.Pass()),
       label_(label),
+      impl_(new ViewTreeHostImpl(registry, this)),
+      host_binding_(impl_.get(), view_tree_host_request.Pass()),
       weak_factory_(this) {
   DCHECK(view_tree_);
   DCHECK(view_tree_token_);
+
+  view_tree_.set_connection_error_handler(
+      base::Bind(&ViewRegistry::OnViewTreeDied, base::Unretained(registry),
+                 base::Unretained(this), "ViewTree connection closed"));
+  host_binding_.set_connection_error_handler(
+      base::Bind(&ViewRegistry::OnViewTreeDied, base::Unretained(registry),
+                 base::Unretained(this), "ViewTreeHost connection closed"));
 }
 
 ViewTreeState::~ViewTreeState() {}
 
-void ViewTreeState::SetRoot(ViewState* root, uint32_t key) {
+void ViewTreeState::LinkRoot(uint32_t key, std::unique_ptr<ViewStub> root) {
+  DCHECK(!root_);
   DCHECK(root);
-  if (root_ != root) {
-    ResetRoot();
-    root->SetTree(this, key);
-    root_ = root;
-  }
+  DCHECK(!root->is_linked());
+  root->SetTree(this, key);
+  root_ = std::move(root);
 }
 
-void ViewTreeState::ResetRoot() {
-  if (root_) {
-    root_->ResetContainer();
-  }
-  root_ = nullptr;
+std::unique_ptr<ViewStub> ViewTreeState::UnlinkRoot() {
+  DCHECK(root_);
+  root_->Unlink();
+  return std::move(root_);
 }
 
-const std::string& ViewTreeState::FormattedLabel() {
+const std::string& ViewTreeState::FormattedLabel() const {
   if (formatted_label_cache_.empty()) {
     formatted_label_cache_ =
         label_.empty() ? base::StringPrintf("<%d>", view_tree_token_->value)