ash: Fix CT remote view host ownership

View hierarchy takes the ownership of the remote view host.
Replace unique_ptr with raw pointer to avoid double-free.

BUG=925769
TEST=manually

Change-Id: Ic34a87081782d10e4ad42ecfaa9fb6127abf52cb
Reviewed-on: https://chromium-review.googlesource.com/c/1488403Reviewed-by: Mitsuru Oshima (Slow) <oshima@chromium.org>
Commit-Queue: Ryo Hashimoto <hashimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635818}

ash/custom_tab/arc_custom_tab_view.cc

@@ -121,7 +121,7 @@ ArcCustomTabView::ArcCustomTabView(int32_t surface_id, int32_t top_margin)
       surface_id_(surface_id),
       top_margin_(top_margin),
       weak_ptr_factory_(this) {
-  AddChildView(remote_view_host_.get());
+  AddChildView(remote_view_host_);
 }
 
 ArcCustomTabView::~ArcCustomTabView() = default;

ash/custom_tab/arc_custom_tab_view.h

@@ -44,7 +44,7 @@ class ArcCustomTabView : public views::View, public mojom::ArcCustomTabView {
   void ConvertPointFromWindow(aura::Window* window, gfx::Point* point);
 
   mojo::Binding<mojom::ArcCustomTabView> binding_;
-  std::unique_ptr<ws::ServerRemoteViewHost> remote_view_host_;
+  ws::ServerRemoteViewHost* remote_view_host_;
   int32_t surface_id_, top_margin_;
   base::WeakPtrFactory<ArcCustomTabView> weak_ptr_factory_;