Reland with a compilation fix.

We would like to use the EXT_swap_control extension to specify the swap
interval of each drawable independently. However open source drivers do
not expose this extension and instead expose the MESA and SGI versions
that have a global swap interval.

This commit changes the code to use the best swap_control extension it
can, potentially changing the swap interval on each swap buffers on
lesser extensions.

BUG=angleproject:1206

Change-Id: I6c24217c7cfd5e09f60469cc7d6336cd68bc5c32
Reviewed-on: https://chromium-review.googlesource.com/312270Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>