Remove unsafe cast from ImageTransportSurfaceOverlayMac::ScheduleCALayer.

ui/gl/gl_image_io_surface.h

Index: ui/gl/gl_image_io_surface.h
diff --git a/ui/gl/gl_image_io_surface.h b/ui/gl/gl_image_io_surface.h
index 48496b741656a53d2cece98de26e48a89b55bfe7..bf9ae8dd68d682076973ee0652faf067d9d234a9 100644
--- a/ui/gl/gl_image_io_surface.h
+++ b/ui/gl/gl_image_io_surface.h
@@ -71,10 +71,14 @@ class GL_EXPORT GLImageIOSurface : public GLImage {
 
   static unsigned GetInternalFormatForTesting(gfx::BufferFormat format);
 
+  // Downcasts from |image|. Returns |nullptr| on failure.
+  static GLImageIOSurface* FromGLImage(GLImage* image);
+
  protected:
   ~GLImageIOSurface() override;
 
  private:
+  Type GetType() const override;
   class RGBConverter;
 
   const gfx::Size size_;