Bug 1612941 - make WR report shader name and features in output for interop with SWGL. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D65595

--HG--
extra : moz-landing-system : lando

gfx/wr/webrender/src/device/gl.rs

@@ -270,8 +270,21 @@ fn build_shader_prefix_string<F: FnMut(&str)>(
     // GLSL requires that the version number comes first.
     output(gl_version_string);
 
+    let mut features_key = String::new();
+    for feat in features.lines() {
+        const PREFIX: &'static str = "#define WR_FEATURE_";
+        if let Some(i) = feat.find(PREFIX) {
+            if i + PREFIX.len() < feat.len() {
+                if !features_key.is_empty() {
+                    features_key.push_str("_");
+                }
+                features_key.push_str(&feat[i + PREFIX.len() ..]);
+            }
+        }
+    }
+
     // Insert the shader name to make debugging easier.
-    let name_string = format!("// {}\n", base_filename);
+    let name_string = format!("// shader: {} {}\n", base_filename, features_key);
     output(&name_string);
 
     // Define a constant depending on whether we are compiling VS or FS.