Always mark *_Base configurations as abstract. These configurations were showing up in generated projects that angle is included in because those projects don't see our common.gypi file that marks these configurations as abstract. Change-Id: I2c93e82567619d23f8535bd4f77446a1f837707f Reviewed-on: https://chromium-review.googlesource.com/270282 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>