Auto merge of #13102 - anholt:webgl-is-program, r=emilio

webgl: Add isProgram() support.

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webgl: Add isProgram() support.

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- [ ] These changes fix #__ (github issue number if applicable).

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There's one failure still, where a deleted program should still be
considered to be a program until it's unbound.  However, I recently
made it so that we unbind at delete time, and we may need to partially
back that change out.

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components/script/dom/webglrenderingcontext.rs

@@ -1403,6 +1403,11 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
         frame_buffer.map_or(false, |buf| buf.target().is_some() && !buf.is_deleted())
     }
 
+    // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
+    fn IsProgram(&self, program: Option<&WebGLProgram>) -> bool {
+        program.map_or(false, |p| !p.is_deleted())
+    }
+
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.7
     fn IsRenderbuffer(&self, render_buffer: Option<&WebGLRenderbuffer>) -> bool {
         render_buffer.map_or(false, |buf| buf.ever_bound() && !buf.is_deleted())