Auto merge of #16893 - MortimerGoro:webgl_extensions, r=emilio

Implement WebGL extensions

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This PR provides the base for implementing WebGL extensions. It comes with the following ones already implemented and passing all related WebGL conformance tests:

- OES_texture_float
- OES_texture_float_linear
- OES_texture_half_float
- OES_texture_half_float_linear
- OES_vertex_array_object

I'll submit other extensions like compressed textures in a separate PR to ease the review process. I included the 5 extensions in this PR because it's easier to show/review how the WebGL extension base works.

To pass all OES_texture_float_xxx tests I had to add some missing format conversions in WebGLRenderingContext.rs

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- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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1 files changed, 26 insertions, 0 deletions

diff --git a/components/script/dom/webgl_extensions/extension.rs b/components/script/dom/webgl_extensions/extension.rs
new file mode 100644
index 00000000000..3463a1d3273
--- /dev/null
+++ b/components/script/dom/webgl_extensions/extension.rs
@@ -0,0 +1,26 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use dom::bindings::js::Root;
+use dom::bindings::reflector::DomObject;
+use dom::bindings::trace::JSTraceable;
+use dom::webglrenderingcontext::WebGLRenderingContext;
+use super::WebGLExtensions;
+
+/// Trait implemented by WebGL extensions.
+pub trait WebGLExtension: Sized where Self::Extension: DomObject + JSTraceable {
+    type Extension;
+
+    /// Creates the DOM object of the WebGL extension.
+    fn new(ctx: &WebGLRenderingContext) -> Root<Self::Extension>;
+
+    /// Checks if the extension is supported.
+    fn is_supported(ext: &WebGLExtensions) -> bool;
+
+    /// Enable the extension.
+    fn enable(ext: &WebGLExtensions);
+
+    /// Name of the WebGL Extension.
+    fn name() -> &'static str;
+}