Support rendering Android Native Pages in VR Shell.

chrome/browser/android/vr_shell/vr_compositor.cc

 // Copyright 2016 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 "chrome/browser/android/vr_shell/vr_compositor.h"
 
+#include <utility>
+
 #include "cc/layers/layer.h"
+#include "cc/layers/solid_color_layer.h"
 #include "content/public/browser/android/compositor.h"
 #include "content/public/browser/web_contents.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/android/window_android.h"
 
 namespace vr_shell {
 
 VrCompositor::VrCompositor(ui::WindowAndroid* window, bool transparent)
     : background_color_(SK_ColorWHITE),
       transparent_(transparent) {
   compositor_.reset(content::Compositor::Create(this, window));
   compositor_->SetHasTransparentBackground(transparent);
 }
 
 VrCompositor::~VrCompositor() {
-  if (layer_)
-    RestoreLayer();
+  RestoreLayer();
 }
 
 void VrCompositor::UpdateLayerTreeHost() {}
 
 void VrCompositor::OnSwapBuffersCompleted(int pending_swap_buffers) {}
 
 void VrCompositor::SetLayer(content::WebContents* web_contents) {
-  if (layer_)
-    RestoreLayer();
+  RestoreLayer();
+  if (!web_contents) {
+    scoped_refptr<cc::SolidColorLayer> layer = cc::SolidColorLayer::Create();
+    layer->SetBackgroundColor(SK_ColorTRANSPARENT);
+    compositor_->SetRootLayer(std::move(layer));
+    return;
+  }
   ui::ViewAndroid* view_android = web_contents->GetNativeView();
 
   // When we pass the layer for the ContentViewCore to the compositor it may be
   // removing it from its previous parent, so we remember that and restore it to
   // its previous parent on teardown.
   layer_ = view_android->GetLayer();
 
   // Remember the old background color to be restored later.
   background_color_ = layer_->background_color();
   if (transparent_) {
     layer_->SetBackgroundColor(SK_ColorTRANSPARENT);
   }
   layer_parent_ = layer_->parent();
   compositor_->SetRootLayer(layer_);
 }
 
 void VrCompositor::RestoreLayer() {
+  if (!layer_)
+    return;
   layer_->SetBackgroundColor(background_color_);
   if (layer_parent_) {
     layer_parent_->AddChild(layer_);
   }
+  layer_ = nullptr;
 }
 
 void VrCompositor::SurfaceDestroyed() {
   compositor_->SetSurface(nullptr);
 }
 
 void VrCompositor::SetWindowBounds(gfx::Size size) {
   compositor_->SetWindowBounds(size);
 }
 
 void VrCompositor::SurfaceChanged(jobject surface) {
-  DCHECK(surface);
   compositor_->SetSurface(surface);
 }
 
 }  // namespace vr_shell