Allow putting NV12 software GMBs into overlays on windows

ui/gl/gl_image_memory.h

Index: ui/gl/gl_image_memory.h
diff --git a/ui/gl/gl_image_memory.h b/ui/gl/gl_image_memory.h
index 1569bcf768b5d4943b3e70d61a3956ce08653355..22b22e4e4e98cd69676df2f3f38df4793189f8de 100644
--- a/ui/gl/gl_image_memory.h
+++ b/ui/gl/gl_image_memory.h
@@ -24,6 +24,9 @@ class GL_EXPORT GLImageMemory : public GLImage {
                   gfx::BufferFormat format,
                   size_t stride);
 
+  // Safe downcast. Returns |nullptr| on failure.
+  static GLImageMemory* FromGLImage(GLImage* image);
+
   // Overridden from GLImage:
   gfx::Size GetSize() override;
   unsigned GetInternalFormat() override;
@@ -39,15 +42,17 @@ class GL_EXPORT GLImageMemory : public GLImage {
                             const gfx::Rect& bounds_rect,
                             const gfx::RectF& crop_rect) override;
   void Flush() override {}
+  Type GetType() const override;
 
   static unsigned GetInternalFormatForTesting(gfx::BufferFormat format);
 
+  const unsigned char* memory() { return memory_; }
+  size_t stride() const { return stride_; }
+  gfx::BufferFormat format() const { return format_; }
+
  protected:
   ~GLImageMemory() override;
 
-  gfx::BufferFormat format() const { return format_; }
-  size_t stride() const { return stride_; }
-
  private:
   const gfx::Size size_;
   const unsigned internalformat_;