Projection Layer not allocation correct-size texture on desktop browser w/ WebXR Emulator

[davehill00]

When running with the Layers polyfill on a desktop browser (Windows Chrome) and the Immersive Web Emulator, the projection layer doesn't seem to be allocating an appropriately sized render target.

More specifically, when running in this mode, both left and right eye are rendered to the projection layer. However, the width of the projection layer is allocated with the width of the browser window. Then, this is split in half and the left eye is rendered to the one half, and the right eye is rendered to the other half. Finally, when the projection layer "renders" out to the screen, the half of the texture that the left eye renders to is stretched to cover the entire browser window.

You can see this in the attached Spector.js trace. I've also attached a Spector.js trace from an app that is not using projection layers for comparison -- it only renders one eye, and renders it to the full-width render target.
projection_layer_polyfill_issue.zip