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}

skia/BUILD.gn

@@ -54,12 +54,15 @@ config("skia_config") {
   }
 
   defines = [
-    "SK_GL",
     "SK_HAS_PNG_LIBRARY",
     "SK_HAS_WEBP_LIBRARY",
     "SK_USER_CONFIG_HEADER=\"../../skia/config/SkUserConfig.h\"",
   ]
 
+  if (skia_use_gl) {
+    defines += [ "SK_GL" ]
+  }
+
   if (!is_ios) {
     defines += [ "SK_HAS_JPEG_LIBRARY" ]
     if (enable_skia_wuffs_gif) {
@@ -569,6 +572,9 @@ component("skia") {
     sources += skia_gpu_sources
     sources += skia_null_gpu_sources
     sources += skia_sksl_gpu_sources
+    if (skia_use_gl) {
+      sources += skia_gl_gpu_sources
+    }
     if (enable_vulkan) {
       sources += skia_vk_sources
       sources += [

skia/features.gni

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