Advertise EGL_EXT_platform_base.
Advertise EGL_EXT_platform_base.

We were not advertising the extension, though we require it for
ANGLE_platform_angle. This was blocking dEQP functionality.

Change-Id: I8781867e772b4b1af62f1387faa863f8ce21de76
Reviewed-on: https://chromium-review.googlesource.com/238082
Tested-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

mlfarrell/angle,mikolalysenko/angle,vvuk/angle,ghostoy/angle,larsbergstrom/angle,ghostoy/angle,ecoal95/angle,larsbergstrom/angle,bsergean/angle,crezefire/angle,MSOpenTech/angle,mikolalysenko/angle,mrobinson/rust-angle,larsbergstrom/angle,mlfarrell/angle,domokit/waterfall,csa7mdm/angle,mrobinson/rust-angle,crezefire/angle,vvuk/angle,ghostoy/angle,mrobinson/rust-angle,mybios/angle,domokit/waterfall,csa7mdm/angle,mrobinson/rust-angle,mybios/angle,mybios/angle,MSOpenTech/angle,csa7mdm/angle,vvuk/angle,csa7mdm/angle,mrobinson/rust-angle,ppy/angle,MSOpenTech/angle,mikolalysenko/angle,crezefire/angle,crezefire/angle,bsergean/angle,ecoal95/angle,MSOpenTech/angle,ecoal95/angle,ecoal95/angle,bsergean/angle,ghostoy/angle,ppy/angle,mlfarrell/angle,larsbergstrom/angle,ppy/angle,ecoal95/angle,mlfarrell/angle,vvuk/angle,ppy/angle,bsergean/angle,mybios/angle,mikolalysenko/angle