Don't enable/disable sRGB on GLES.
Don't enable/disable sRGB on GLES.

glEnable/glDisable GL_FRAMEBUFFER_SRGB isn't meaningful on GLES.

BUG=angleproject:1300

Change-Id: I0afd697ed9770e2eb1cdcc851884b90de1a4583c
Reviewed-on: https://chromium-review.googlesource.com/334490
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Commit-Queue: Frank Henigman <4f3ccfa167f952ff7263448ff4377acff6a23e5c@chromium.org>

ppy/angle,ppy/angle,MSOpenTech/angle,MSOpenTech/angle,ecoal95/angle,domokit/waterfall,ecoal95/angle,ecoal95/angle,domokit/waterfall,ppy/angle,mikolalysenko/angle,mikolalysenko/angle,MSOpenTech/angle,ecoal95/angle,ecoal95/angle,ppy/angle,MSOpenTech/angle,mikolalysenko/angle,mikolalysenko/angle