Add skia GL-only build constructs.

A pending change to skia will delineate GL-only sources from
multi-GPU interface source lists in the build configuration.
This change serializes the integration of that change between
the two repos.

Change-Id: I12bdc14228fbc9bd56214301fa7ab02eff5b2efc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1910870
Commit-Queue: John Rosasco <rosasco@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Cr-Commit-Position: refs/heads/master@{#714590}

diff --git a/skia/features.gni b/skia/features.gni
index f8ee32ea..2a94ac2 100644
--- a/skia/features.gni
+++ b/skia/features.gni

@@ -5,4 +5,5 @@
 declare_args() {
   # Enable experimental SkiaRenderer Dawn backend.
   skia_use_dawn = false
+  skia_use_gl = true
 }