Visually disable VR Shell back/forward buttons when no history is available

chrome/browser/android/vr_shell/vr_shell.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_shell.h"
 
 #include <android/native_window_jni.h>
 
 #include <string>
 #include <utility>
@@ skipping 348 matching lines @@
   content_surface_ = nullptr;
   return surface;
 }
 
 void VrShell::RestoreContentSurface(JNIEnv* env,
                                     const JavaParamRef<jobject>& obj) {
   PostToGlThreadWhenReady(
       base::Bind(&VrShellGl::CreateContentSurface, gl_thread_->GetVrShellGl()));
 }
 
+void VrShell::SetHistoryButtonsEnabled(JNIEnv* env,
+                                       const JavaParamRef<jobject>& obj,
+                                       jboolean can_go_back,
+                                       jboolean can_go_forward) {
+  html_interface_->SetHistoryButtonsEnabled(can_go_back, can_go_forward);
+}
+
 void VrShell::UiSurfaceChanged(jobject surface) {
   ui_compositor_->SurfaceChanged(surface);
 }
 
 void VrShell::ContentSurfaceChanged(jobject surface) {
   content_surface_ = surface;
   content_compositor_->SurfaceChanged(surface);
   JNIEnv* env = base::android::AttachCurrentThread();
   Java_VrShellImpl_contentSurfaceChanged(env, j_vr_shell_.obj());
 }
@@ skipping 308 matching lines @@
            jboolean reprojected_rendering) {
   return reinterpret_cast<intptr_t>(new VrShell(
       env, obj, reinterpret_cast<ui::WindowAndroid*>(content_window_android),
       content::WebContents::FromJavaWebContents(ui_web_contents),
       reinterpret_cast<ui::WindowAndroid*>(ui_window_android), for_web_vr,
       VrShellDelegate::GetNativeVrShellDelegate(env, delegate),
       reinterpret_cast<gvr_context*>(gvr_api), reprojected_rendering));
 }
 
 }  // namespace vr_shell