Implement a means of letting native VR Shell control the HTML UI.

chrome/browser/android/vr_shell/ui_interface.h

Index: chrome/browser/android/vr_shell/ui_interface.h
diff --git a/chrome/browser/android/vr_shell/ui_interface.h b/chrome/browser/android/vr_shell/ui_interface.h
new file mode 100644
index 0000000000000000000000000000000000000000..a0ea5661766e3bb3a0a527a3d4aa7551da04c6d3
--- /dev/null
+++ b/chrome/browser/android/vr_shell/ui_interface.h
@@ -0,0 +1,48 @@
+// 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.
+
+#ifndef CHROME_BROWSER_ANDROID_VR_SHELL_UI_INTERFACE_H_
+#define CHROME_BROWSER_ANDROID_VR_SHELL_UI_INTERFACE_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/values.h"
+
+class VrShellUIMessageHandler;
+
+namespace vr_shell {
+
+// This class manages the communication of browser state from VR shell to the
+// HTML UI. State information is asynchronous and unidirectional.
+class UiInterface {
+ public:
+  enum Mode {
+    STANDARD,
+    WEB_VR,
+  };
+
+  UiInterface();
+  virtual ~UiInterface();
+
+  void SetMode(Mode mode);
+  void SetSecureOrigin(bool secure);
+
+  // Called by WebUI when starting VR.
+  void OnDomContentsLoaded();
+  void SetUiMessageHandler(
+      base::WeakPtr<VrShellUIMessageHandler> handler);
+
+ private:
+  void FlushUpdates();
+
+  base::WeakPtr<VrShellUIMessageHandler> handler_;

[bshe, 2016/10/19 21:02:40]

do you need a weakptr here? My guess is that this class will out live
VrShellUIMessageHandler. And you can probably set it to null in the dtor of
VrShellUIMessageHandler since you are able to access this through
vr_shell->GetUiInterface. If VrShellUIMessageHandler out live this class, you
don't need a weakptr either.

[cjgrant, 2016/10/20 15:25:39]

Done.  Good call on use of the handler destructor.

+  base::DictionaryValue updates_;

[bshe, 2016/10/19 21:02:40]

nit: looks like this is the global states. Perhaps rename it to states_. And I
would also prefer only do update on change.

[cjgrant, 2016/10/20 15:25:39]

As discussed, the dictionary isn't maintaining state, other than when VR
launches.  I missed clearing it after a flush.  Thanks for catching that.

+  bool loaded_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(UiInterface);
+};
+
+}  // namespace vr_shell
+
+#endif  // CHROME_BROWSER_ANDROID_VR_SHELL_UI_INTERFACE_H_