gpu: Disallow use of IOSurfaces for half-float format with swiftshader.

R=kbr@chromium.org

Bug: 998038
Change-Id: Ic31d28938ef205b36657fc7bd297fe8a63d08543
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1798052
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Auto-Submit: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695826}
void FeatureInfo::EnableCHROMIUMTextureStorageImage() {
  if (!feature_flags_.chromium_texture_storage_image) {
    feature_flags_.chromium_texture_storage_image = true;
    AddExtensionString("GL_CHROMIUM_texture_storage_image");
  }
}

void FeatureInfo::EnableCHROMIUMTextureStorageImage() {
  if (!feature_flags_.chromium_texture_storage_image) {
    feature_flags_.chromium_texture_storage_image = true;
    AddExtensionString("GL_CHROMIUM_texture_storage_image");
  }
}
