Image Loading: `crossorigin` mutations should queue a microtask

This CL makes HTMLImageElement aware of `crossorigin` attribute value
mutations, and respond by invoking ImageLoader::UpdateFromElement if
the attribute's state changes. This queues a microtask to finish the
image loading steps.

This change does not influence the crossorigin attribute state used to
influence any image request, because the crossorigin attribute state
used to configure image requests (in blink::ConfigureRequest) is already
referring to the element's latest. Instead, this change simply invokes
ImageLoader::UpdateFromElement (enqueueing an ImageLoader::Task
microtask) when an image's crossorigin attribute state changes, even
after an image has been fetched.

This makes our implementation of the HTML Standard's image element's
relevant mutations [1] more compliant, passing more relevant mutations
web-platform-tests. See also [2].

[1]: https://html.spec.whatwg.org/multipage/images.html#relevant-mutations
[2]: https://docs.google.com/document/d/1Xp34FIbbZnJILl0PNd1sfs_3z1HSriUVyRUgnAesGZk/

Bug: 384251,774706,1061685
Change-Id: I11e66800309df96aea61226932b9aa40c3cc5d27
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2102992
Commit-Queue: Dominic Farolino <dom@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750885}

third_party/blink/renderer/core/html/html_image_element.cc

@@ -39,6 +39,7 @@
 #include "third_party/blink/renderer/core/frame/deprecation.h"
 #include "third_party/blink/renderer/core/frame/local_dom_window.h"
 #include "third_party/blink/renderer/core/html/canvas/html_canvas_element.h"
+#include "third_party/blink/renderer/core/html/cross_origin_attribute.h"
 #include "third_party/blink/renderer/core/html/forms/form_associated.h"
 #include "third_party/blink/renderer/core/html/forms/html_form_element.h"
 #include "third_party/blink/renderer/core/html/html_dimension.h"
@@ -288,6 +289,24 @@ void HTMLImageElement::ParseAttribute(
     // |importance| attribute to the loading pipeline takes place in
     // ImageLoader.
     UseCounter::Count(GetDocument(), WebFeature::kPriorityHints);
+  } else if (name == html_names::kCrossoriginAttr) {
+    // As per an image's relevant mutations [1], we must queue a new loading
+    // microtask when the `crossorigin` attribute state has changed. Note that
+    // the attribute value can change without the attribute state changing [2].
+    //
+    // [1]:
+    // https://html.spec.whatwg.org/multipage/images.html#relevant-mutations
+    // [2]: https://github.com/whatwg/html/issues/4533#issuecomment-483417499
+    CrossOriginAttributeValue new_crossorigin_state =
+        GetCrossOriginAttributeValue(params.new_value);
+    CrossOriginAttributeValue old_crossorigin_state =
+        GetCrossOriginAttributeValue(params.old_value);
+
+    if (new_crossorigin_state != old_crossorigin_state) {
+      // Update the current state so we can detect future state changes.
+      GetImageLoader().UpdateFromElement(
+          ImageLoader::kUpdateIgnorePreviousError, referrer_policy_);
+    }
   } else {
     HTMLElement::ParseAttribute(params);
   }

third_party/blink/web_tests/external/wpt/html/semantics/embedded-content/the-img-element/relevant-mutations-expected.txt

 This is a testharness.js-based test.
-Found 81 tests; 64 PASS, 17 FAIL, 0 TIMEOUT, 0 NOTRUN.
+Found 81 tests; 74 PASS, 7 FAIL, 0 TIMEOUT, 0 NOTRUN.
 PASS src set
 PASS src changed
 PASS src removed
@@ -20,16 +20,16 @@ PASS crossorigin anonymous to use-credentials, src absent
 PASS crossorigin use-credentials to absent, src absent
 PASS crossorigin use-credentials to empty, src absent
 PASS crossorigin use-credentials to anonymous, src absent
-FAIL crossorigin absent to empty, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin absent to anonymous, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin absent to use-credentials, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin empty to absent, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin empty to use-credentials, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin anonymous to absent, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin anonymous to use-credentials, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin use-credentials to absent, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin use-credentials to empty, src already set assert_unreached: update the image data didn't run Reached unreachable code
-FAIL crossorigin use-credentials to anonymous, src already set assert_unreached: update the image data didn't run Reached unreachable code
+PASS crossorigin absent to empty, src already set
+PASS crossorigin absent to anonymous, src already set
+PASS crossorigin absent to use-credentials, src already set
+PASS crossorigin empty to absent, src already set
+PASS crossorigin empty to use-credentials, src already set
+PASS crossorigin anonymous to absent, src already set
+PASS crossorigin anonymous to use-credentials, src already set
+PASS crossorigin use-credentials to absent, src already set
+PASS crossorigin use-credentials to empty, src already set
+PASS crossorigin use-credentials to anonymous, src already set
 FAIL inserted into picture assert_unreached: update the image data didn't run Reached unreachable code
 FAIL removed from picture assert_unreached: update the image data didn't run Reached unreachable code
 PASS parent is picture, previous source inserted