ANGLETest: When on WebGL compatibility then use index buffers WebGL actually requires the use of index buffers, otherwise the call is invalid, therefore explicitely request index buffers in the according VertexAttributeOORTest tests. In addition, assert on the indices when the glDrawElements call is captured. With that we can enable VertexAttributeOORTest.* Bug: angleproject:6125 Change-Id: Id3855c78d4c5fcab5599f19dd74ce745d059fb1c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2999523 Commit-Queue: Gert Wollny <gert.wollny@collabora.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>