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

chrome/browser/resources/vr_shell/vr_shell_ui_api.js

Index: chrome/browser/resources/vr_shell/vr_shell_ui_api.js
diff --git a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
index 30f50da1dbed737672bfa254fdc39aa253f201e1..d4fe306a670a9fb9b3d7505d957fca1298ac0fc5 100644
--- a/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
+++ b/chrome/browser/resources/vr_shell/vr_shell_ui_api.js
@@ -627,6 +627,13 @@ api.NativeCommandHandler = class {
   onRemoveTab(tab) {}
 
   /**
+   * Set back/forward history buttons to enabled/disabled

[mthiesse, 2017/03/08 16:15:18]

Nit: period at the end of sentences in comments

[acondor_, 2017/03/08 16:42:26]

Done.

+   * @param {boolean} canGoBack
+   * @param {boolean} canGoForward
+   */
+  onSetHistoryButtonsEnabled(canGoBack, canGoForward) {}
+
+  /**
    * This function is executed after command parsing completes.
    */
   onCommandHandlerFinished() {}
@@ -673,6 +680,9 @@ api.NativeCommandHandler = class {
     if ('removeTab' in dict) {
       this.onRemoveTab(dict['removeTab']);
     }
+    if ('canGoBack' in dict) {
+      this.onSetHistoryButtonsEnabled(dict['canGoBack'], dict['canGoForward']);
+    }
 
     this.onCommandHandlerFinished()
   }