Fix standalone compilation on Mac Apple Clang 8.1 doesn't allow implicit conversion from gl::Error to egl::Error with the egl::Error::Error(gl::Error&&) constructor. Same thing for gl and egl reversed. This commits add conversion constructors taking errors by value. There should be not performance impact for non-error code paths. BUG= Change-Id: I91acf094af923080780b91850146d71016ec5ebc Reviewed-on: https://chromium-review.googlesource.com/671284 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>