Bug 1592044 - Add MozFramebuffer::HasDepth() and HasStencil(). r=jgilbert

Differential Revision: https://phabricator.services.mozilla.com/D55040

--HG--
extra : moz-landing-system : lando

gfx/gl/MozFramebuffer.h

@@ -49,6 +49,8 @@ class MozFramebuffer final {
     if (mColorTarget == LOCAL_GL_RENDERBUFFER) return 0;
     return mColorName;
   }
+  bool HasDepth() const { return mDepthRB; }
+  bool HasStencil() const { return mStencilRB; }
 };
 
 }  // namespace gl