Don't enable GL backends by default if build_with_chromium

This is the simplest change necessary to remove GL backends from
the build in Chrome. The backends will still be enabled on bots
that test Dawn. A more proper fix might be to update the dawn.py
recipe to explicitly enable the GLES backend (we don't test the
GL backend on bots using dawn.py, but we do test GLES), and then
defaulting both dawn_enable_desktop_gl and dawn_enable_opengles
to false.

For now, stick with the most minimal change for two reasons:
 1. Defaulting to false would lose automatically enabling the
    backends in Dawn standalone builds where they're supported.
 2. LUCI changes have changed the permissions to trigger tryjobs
    on recipe changes, so testing a recipe change is not possible
    right now. See crbug.com/1168315.

Bug: dawn:1036
Change-Id: I7f4977fbd271200f1d6161d2e2b3438cdb4db1ca
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/61600
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

scripts/dawn_features.gni

@@ -62,13 +62,13 @@ declare_args() {
 
   # Enables the compilation of Dawn's OpenGL backend
   # (best effort, non-conformant)
-  dawn_enable_desktop_gl = is_linux && !is_chromeos
+  dawn_enable_desktop_gl = !build_with_chromium && (is_linux && !is_chromeos)
 
   # Enables the compilation of Dawn's OpenGLES backend
   # (WebGPU/Compat subset)
   # Disables OpenGLES when compiling for UWP, since UWP only supports d3d
-  dawn_enable_opengles =
-      (is_linux && !is_chromeos) || (is_win && !dawn_is_winuwp)
+  dawn_enable_opengles = !build_with_chromium && ((is_linux && !is_chromeos) ||
+                                                  (is_win && !dawn_is_winuwp))
 
   # Enables the compilation of Dawn's Vulkan backend
   # Disables vulkan when compiling for UWP, since UWP only supports d3d