Add support for WebGL2 GetFragDataLocation

Adds support for the `GetFragDataLocation` WebGL2 call.

See: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.7

components/script/dom/webgl2renderingcontext.rs

@@ -1467,6 +1467,12 @@ impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
         self.base.GetAttribLocation(program, name)
     }
 
+    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.7
+    fn GetFragDataLocation(&self, program: &WebGLProgram, name: DOMString) -> i32 {
+        handle_potential_webgl_error!(self.base, self.base.validate_ownership(program), return -1);
+        handle_potential_webgl_error!(self.base, program.get_frag_data_location(name), -1)
+    }
+
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
     fn GetProgramInfoLog(&self, program: &WebGLProgram) -> Option<DOMString> {
         self.base.GetProgramInfoLog(program)

components/script/dom/webglprogram.rs

@@ -365,6 +365,30 @@ impl WebGLProgram {
         Ok(location)
     }
 
+    /// glGetFragDataLocation
+    pub fn get_frag_data_location(&self, name: DOMString) -> WebGLResult<i32> {
+        if !self.is_linked() || self.is_deleted() {
+            return Err(WebGLError::InvalidOperation);
+        }
+
+        if !validate_glsl_name(&name)? {
+            return Ok(-1);
+        }
+        if name.starts_with("gl_") {
+            return Ok(-1);
+        }
+
+        let (sender, receiver) = webgl_channel().unwrap();
+        self.upcast::<WebGLObject>()
+            .context()
+            .send_command(WebGLCommand::GetFragDataLocation(
+                self.id,
+                name.into(),
+                sender,
+            ));
+        Ok(receiver.recv().unwrap())
+    }
+
     /// glGetUniformLocation
     pub fn get_uniform_location(
         &self,

components/script/dom/webidls/WebGL2RenderingContext.webidl

@@ -422,7 +422,7 @@ interface mixin WebGL2RenderingContextBase
   //                              optional GLuint srcLengthOverride = 0);
 
   /* Programs and shaders */
-  // [WebGLHandlesContextLoss] GLint getFragDataLocation(WebGLProgram program, DOMString name);
+  [WebGLHandlesContextLoss] GLint getFragDataLocation(WebGLProgram program, DOMString name);
 
   /* Uniforms */
   void uniform1ui(WebGLUniformLocation? location, GLuint v0);