Reland: Remove unsafe cast from ImageTransportSurfaceOverlayMac::ScheduleCALayer.

ui/gl/gl_image.h

 // Copyright (c) 2012 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 UI_GL_GL_IMAGE_H_
 #define UI_GL_GL_IMAGE_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 67 matching lines @@
   // CHROMIUM image with internalformat GL_RGB, but the platform only supports
   // GL_RGBA. The client is responsible for implementing appropriate
   // workarounds. The only support that the command buffer provides is format
   // validation during calls to copyTexImage2D and copySubTexImage2D.
   //
   // This is a workaround that is not intended to become a permanent part of the
   // GLImage API. Theoretically, when Apple fixes their drivers, this can be
   // removed. https://crbug.com/581777#c36
   virtual bool EmulatingRGB() const;
 
+  // An identifier for subclasses. Necessary for safe downcasting.
+  enum class Type {
+    NONE,
+    IOSURFACE
+  };
+  virtual Type GetType() const;
+
  protected:
   virtual ~GLImage() {}
 
  private:
   friend class base::RefCounted<GLImage>;
 
   DISALLOW_COPY_AND_ASSIGN(GLImage);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_IMAGE_H_