Issue #1620 - Use Intrinsic Aspect Ratio for Images

https://bugzilla.mozilla.org/show_bug.cgi?id=1547231
https://bugzilla.mozilla.org/show_bug.cgi?id=1559094
https://bugzilla.mozilla.org/show_bug.cgi?id=1633434
https://bugzilla.mozilla.org/show_bug.cgi?id=1565690
https://bugzilla.mozilla.org/show_bug.cgi?id=1602047

Make use of Aspect Ratios in Image frames before Images are loaded.
- Check for width and height HTML properties and create a ratio with them.
- Overwrite HTML size values with actual image dimensions on load.
- Collapse any frames with srcless images.

Comments:
dom/html/nsGenericHTMLElement.cpp:1483
layout/generic/nsImageFrame.cpp:289

modules/libpref/init/all.js

@@ -4819,6 +4819,12 @@ pref("media.ondevicechange.fakeDeviceChangeEvent.enabled", false);
 // those platforms we don't handle touch events anyway so it's conceptually
 // a no-op.
 pref("layout.css.touch_action.enabled", true);
+ 
+// WHATWG computed intrinsic aspect ratio for an img element
+// https://html.spec.whatwg.org/multipage/rendering.html#attributes-for-embedded-content-and-images
+// Are the width and height attributes on image-like elements mapped to the
+// internal-for-now aspect-ratio property?
+pref("layout.css.width-and-height-map-to-aspect-ratio.enabled", false);
 
 // Enables some assertions in nsStyleContext that are too expensive
 // for general use, but might be useful to enable for specific tests.