Enable gpu rasterization in the vr shell

chrome/browser/android/vr_shell/ui_elements/ui_element.h

Index: chrome/browser/android/vr_shell/ui_elements/ui_element.h
diff --git a/chrome/browser/android/vr_shell/ui_elements/ui_element.h b/chrome/browser/android/vr_shell/ui_elements/ui_element.h
index da5d829c4cab8cf7bf62d7f299cf9c309f05d8e4..5948fea688c2ab39493b281f8b44407a27d2e6a2 100644
--- a/chrome/browser/android/vr_shell/ui_elements/ui_element.h
+++ b/chrome/browser/android/vr_shell/ui_elements/ui_element.h
@@ -20,6 +20,7 @@ namespace vr_shell {
 
 class Animation;
 class VrShellRenderer;
+class VrSurfaceProvider;
 
 enum XAnchoring {
   XNONE = 0,
@@ -104,7 +105,7 @@ class UiElement : public WorldRectangle {
   virtual void Render(VrShellRenderer* renderer,
                       vr::Mat4f view_proj_matrix) const;
 
-  virtual void Initialize();
+  void Initialize(VrSurfaceProvider* provider);
 
   // Controller interaction methods.
   virtual void OnHoverEnter();
@@ -219,6 +220,12 @@ class UiElement : public WorldRectangle {
   bool dirty() const { return dirty_; }
   void set_dirty(bool dirty) { dirty_ = dirty; }
 
+ protected:
+  virtual void Initialize();
+
+  // This obtains a GPU-backed surface. Only valid after initialized.
+  VrSurfaceProvider* surface_provider() { return surface_provider_; }
+
  private:
   // Valid IDs are non-negative.
   int id_ = -1;
@@ -285,6 +292,8 @@ class UiElement : public WorldRectangle {
 
   Transform transform_;
 
+  VrSurfaceProvider* surface_provider_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(UiElement);
 };