Re-reland with a warning 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: I7ecf1eed6808672f277d0242d65f90d7851d2a32
Reviewed-on: https://chromium-review.googlesource.com/312322
Tryjob-Request: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>