Bug 1623074 - add debug shaders to SWGL build. r=jrmuizel

Depends on D92909

Differential Revision: https://phabricator.services.mozilla.com/D92910

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/84734d70cba39d079ee3cda25ceefe41e2268c98

swgl/build.rs

@@ -112,7 +112,8 @@ fn main() {
 
     let shader_flags =
         ShaderFeatureFlags::GL |
-        ShaderFeatureFlags::DUAL_SOURCE_BLENDING;
+        ShaderFeatureFlags::DUAL_SOURCE_BLENDING |
+        ShaderFeatureFlags::DEBUG;
     let mut shaders: Vec<String> = Vec::new();
     for (name, features) in get_shader_features(shader_flags) {
         shaders.extend(features.iter().map(|f| {

webrender_build/src/shader_features.rs

@@ -15,6 +15,7 @@ bitflags! {
         const PIXEL_LOCAL_STORAGE = 1 << 10;
         const DITHERING = 1 << 11;
         const TEXTURE_EXTERNAL = 1 << 12;
+        const DEBUG = 1 << 13;
     }
 }
 
@@ -200,6 +201,12 @@ pub fn get_shader_features(flags: ShaderFeatureFlags) -> ShaderFeatures {
 
     shaders.insert("ps_clear", vec![base_prim_features.finish()]);
 
+    if flags.contains(ShaderFeatureFlags::DEBUG) {
+        for name in &["debug_color", "debug_font"] {
+            shaders.insert(name, vec![String::new()]);
+        }
+    }
+
     shaders
 }