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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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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1 files changed, 85 insertions, 0 deletions

diff --git a/components/script/dom/webgl_extensions/wrapper.rs b/components/script/dom/webgl_extensions/wrapper.rs
new file mode 100644
index 00000000000..33fdd727529
--- /dev/null
+++ b/components/script/dom/webgl_extensions/wrapper.rs
@@ -0,0 +1,85 @@
+/* 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 core::nonzero::NonZero;
+use dom::bindings::js::{MutNullableJS, Root};
+use dom::bindings::reflector::DomObject;
+use dom::bindings::trace::JSTraceable;
+use dom::webglrenderingcontext::WebGLRenderingContext;
+use heapsize::HeapSizeOf;
+use js::jsapi::JSObject;
+use std::any::Any;
+use super::{WebGLExtension, WebGLExtensions};
+
+/// Trait used internally by WebGLExtensions to store and
+/// handle the different WebGL extensions in a common list.
+pub trait WebGLExtensionWrapper: JSTraceable + HeapSizeOf {
+    fn instance_or_init(&self,
+                        ctx: &WebGLRenderingContext,
+                        ext: &WebGLExtensions)
+                        -> NonZero<*mut JSObject>;
+    fn is_supported(&self, &WebGLExtensions) -> bool;
+    fn enable(&self, ext: &WebGLExtensions);
+    fn name(&self) -> &'static str;
+    fn as_any(&self) -> &Any;
+}
+
+#[must_root]
+#[derive(JSTraceable, HeapSizeOf)]
+pub struct TypedWebGLExtensionWrapper<T: WebGLExtension> {
+    extension: MutNullableJS<T::Extension>
+}
+
+/// Typed WebGL Extension implementation.
+/// Exposes the exact MutNullableJS<DOMObject> type defined by the extension.
+impl<T: WebGLExtension> TypedWebGLExtensionWrapper<T> {
+    pub fn new() -> TypedWebGLExtensionWrapper<T> {
+        TypedWebGLExtensionWrapper {
+            extension: MutNullableJS::new(None)
+        }
+    }
+}
+
+impl<T> WebGLExtensionWrapper for TypedWebGLExtensionWrapper<T>
+                              where T: WebGLExtension + JSTraceable + HeapSizeOf + 'static {
+    #[allow(unsafe_code)]
+    fn instance_or_init(&self,
+                        ctx: &WebGLRenderingContext,
+                        ext: &WebGLExtensions)
+                        -> NonZero<*mut JSObject> {
+        let mut enabled = true;
+        let extension = self.extension.or_init(|| {
+            enabled = false;
+            T::new(ctx)
+        });
+        if !enabled {
+            self.enable(ext);
+        }
+        unsafe {
+            NonZero::new(extension.reflector().get_jsobject().get())
+        }
+    }
+
+    fn is_supported(&self, ext: &WebGLExtensions) -> bool {
+        self.extension.get().is_some() || T::is_supported(ext)
+    }
+
+    fn enable(&self, ext: &WebGLExtensions) {
+        T::enable(ext);
+    }
+
+    fn name(&self) -> &'static str {
+        T::name()
+    }
+
+    fn as_any<'a>(&'a self) -> &'a Any {
+        self
+    }
+}
+
+impl<T> TypedWebGLExtensionWrapper<T> where T: WebGLExtension + JSTraceable + HeapSizeOf + 'static {
+    pub fn dom_object(&self) -> Option<Root<T::Extension>> {
+        self.extension.get()
+    }
+}