Auto merge of #20884 - jdm:more-limits, r=avadacatavra

Don't forward GL parameter gets for constant limits.

This avoids IPC traffic for unchanging constants that are determined when the GL context is created. These changes require https://github.com/emilio/rust-offscreen-rendering-context/pull/123.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #20876.
- [x] There are tests for these changes

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components/script/Cargo.toml

@@ -68,7 +68,7 @@ mozjs = { version = "0.7.1", features = ["promises"]}
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
 num-traits = "0.1.32"
-offscreen_gl_context = {version = "0.16", features = ["serde"]}
+offscreen_gl_context = {version = "0.17", features = ["serde"]}
 parking_lot = "0.5"
 phf = "0.7.18"
 profile_traits = {path = "../profile_traits"}

components/script/dom/webglrenderingcontext.rs

@@ -51,7 +51,7 @@ use euclid::Size2D;
 use fnv::FnvHashMap;
 use half::f16;
 use js::jsapi::{JSContext, JSObject, Type};
-use js::jsval::{BooleanValue, DoubleValue, Int32Value, JSVal, NullValue, UndefinedValue};
+use js::jsval::{BooleanValue, DoubleValue, Int32Value, UInt32Value, JSVal, NullValue, UndefinedValue};
 use js::rust::CustomAutoRooterGuard;
 use js::typedarray::ArrayBufferView;
 use net_traits::image::base::PixelFormat;
@@ -1337,6 +1337,35 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
             _ => {}
         }
 
+        // Handle any MAX_ parameters by retrieving the limits that were stored
+        // when this context was created.
+        let limit = match parameter {
+            constants::MAX_VERTEX_ATTRIBS =>
+                Some(self.limits.max_vertex_attribs),
+            constants::MAX_TEXTURE_SIZE =>
+                Some(self.limits.max_tex_size),
+            constants::MAX_CUBE_MAP_TEXTURE_SIZE =>
+                Some(self.limits.max_cube_map_tex_size),
+            constants::MAX_COMBINED_TEXTURE_IMAGE_UNITS =>
+                Some(self.limits.max_combined_texture_image_units),
+            constants::MAX_FRAGMENT_UNIFORM_VECTORS =>
+                Some(self.limits.max_fragment_uniform_vectors),
+            constants::MAX_RENDERBUFFER_SIZE =>
+                Some(self.limits.max_renderbuffer_size),
+            constants::MAX_TEXTURE_IMAGE_UNITS =>
+                Some(self.limits.max_texture_image_units),
+            constants::MAX_VARYING_VECTORS =>
+                Some(self.limits.max_varying_vectors),
+            constants::MAX_VERTEX_TEXTURE_IMAGE_UNITS =>
+                Some(self.limits.max_vertex_texture_image_units),
+            constants::MAX_VERTEX_UNIFORM_VECTORS =>
+                Some(self.limits.max_vertex_uniform_vectors),
+            _ => None,
+        };
+        if let Some(limit) = limit {
+            return UInt32Value(limit);
+        }
+
         if !self.extension_manager.is_get_parameter_name_enabled(parameter) {
             self.webgl_error(WebGLError::InvalidEnum);
             return NullValue();