Bug 1834110 - Do not run script elements with whitespace type attribute values r=peterv

Fixed running script elements with a type attribute value with whitespace
(like " ").

Fixed by comparing value emptiness before and after trim, if not empty
before and empty after, undo the trim.

2 WPT subtests now newly pass.

WPT tests: https://wpt.fyi/results/html/semantics/scripting-1/the-script-element/script-type-and-language-js.html

Differential Revision: https://phabricator.services.mozilla.com/D178573

dom/html/HTMLScriptElement.cpp

@@ -151,8 +151,17 @@ bool HTMLScriptElement::GetScriptType(nsAString& aType) {
   // ASCII whitespace https://infra.spec.whatwg.org/#ascii-whitespace:
   // U+0009 TAB, U+000A LF, U+000C FF, U+000D CR, or U+0020 SPACE.
   static const char kASCIIWhitespace[] = "\t\n\f\r ";
+
+  const bool wasEmptyBeforeTrim = type.IsEmpty();
   type.Trim(kASCIIWhitespace);
 
+  // If the value before trim was not empty and the value is now empty, do not
+  // trim as we want to retain pure whitespace (by restoring original value)
+  // because we need to treat "" and " " (etc) differently.
+  if (!wasEmptyBeforeTrim && type.IsEmpty()) {
+    return GetAttr(kNameSpaceID_None, nsGkAtoms::type, aType);
+  }
+
   aType.Assign(type);
   return true;
 }

testing/web-platform/meta/html/semantics/scripting-1/the-script-element/script-type-and-language-js-xhtml.xhtml.ini

-[script-type-and-language-js-xhtml.xhtml]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Script shouldn't run with type=" "]
-    expected: FAIL

testing/web-platform/meta/html/semantics/scripting-1/the-script-element/script-type-and-language-js.html.ini

-[script-type-and-language-js.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Script shouldn't run with type=" "]
-    expected: FAIL