According to the latest change in WebGL's OVR_multiview2 spec, the GL_OVR_multiview should NOT be defined. Refer to https://www.khronos.org/registry/webgl/extensions/OVR_multiview2/

I.e. this shader should NOT fail compilation:

#version 300 es
#extension GL_OVR_multiview2 : require
#ifdef GL_OVR_multiview
    #error legacy GL_OVR_multiview support must be forbidden
#endif
....

Bug: angleproject:4279
Change-Id: Ic94cba6785ea3a1fa14d5131dc0960214aa574be
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1994830
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>