For <img src=""> (no current request), do not use mapped aspect ratio.

This works in chrome because they don't event create an image box for this case,
which is totally against the spec.

The spec doesn't consider an image with a null image request, but our behavior
changes in some other places as well because of it...

Depends on D56367

Differential Revision: https://phabricator.services.mozilla.com/D56368

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1602047
gecko-commit: bc309b2cd9e74e1116b82c908e0715741fda3e0e
gecko-integration-branch: autoland
gecko-reviewers: tnikkel

html/rendering/replaced-elements/attributes-for-embedded-content-and-images/img-aspect-ratio.html

@@ -11,6 +11,7 @@
 </style>
 <img src="/images/green.png">
 <img src="/images/green.png" width=100 height=125>
+<img src="" width=100 height=125>
 <script>
 let t = async_test("Image width and height attributes are used to infer aspect-ratio");
 function assert_ratio(img, expected) {
@@ -46,7 +47,8 @@
 
 onload = t.step_func_done(function() {
   let images = document.querySelectorAll("img");
-  assert_ratio(images[2], 1.266); // 1.266 is the original aspect ratio of blue.png
+  assert_ratio(images[3], 1.266); // 1.266 is the original aspect ratio of blue.png
+  assert_equals(getComputedStyle(images[2]).height, "0px"); // aspect-ratio doesn't override intrinsic size of images that don't have any src.
   assert_ratio(images[1], 2.0); // 2.0 is the original aspect ratio of green.png
   assert_ratio(images[0], 2.0); // Loaded image's aspect ratio, at least by default, overrides width / height ratio.
 });