Bug 1703654 - Prototype display-p3 for WebGL canvas. r=lsalzman,emilio

Enable (direct) external surface compositing for MacIOSurfaces.
Works on Mac.

Differential Revision: https://phabricator.services.mozilla.com/D144073

dom/canvas/ClientWebGLContext.cpp

@@ -837,11 +837,19 @@ ClientWebGLContext::SetContextOptions(JSContext* cx,
     newOpts.antialias = attributes.mAntialias.Value();
   }
 
+  if (attributes.mColorSpace.WasPassed()) {
+    newOpts.colorSpace = Some(attributes.mColorSpace.Value());
+  } else if (StaticPrefs::gfx_color_management_native_srgb()) {
+    newOpts.colorSpace = Some(dom::PredefinedColorSpace::Srgb);
+  }
+
   // Don't do antialiasing if we've disabled MSAA.
   if (!StaticPrefs::webgl_msaa_samples()) {
     newOpts.antialias = false;
   }
 
+  // -
+
   if (mInitialOptions && *mInitialOptions != newOpts) {
     // Err if the options asked for aren't the same as what they were
     // originally.