Bug 1719387 - Make `test_bug795418-2.html` request `text/unicode` flavor in the headless mode r=smaug

Until fixing bug 1686012, clipboard in the headless mode does not support
"text/html" flavor.  Therefore, the `waitForClipboard` in the test does not
get expected value as `aData` in the first callback.

So, it should request `text/unicode` in the headless mode.

Depends on D119483

Differential Revision: https://phabricator.services.mozilla.com/D119484

editor/libeditor/tests/test_bug795418-2.html

@@ -27,15 +27,9 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=795418
 /** Test for Bug 795418 **/
 SimpleTest.waitForExplicitFinish();
 SimpleTest.waitForFocus(function() {
-  var div = document.getElementById("copySource");
-  var sel = window.getSelection();
-  sel.removeAllRanges();
-
-  // Select the text from the text node in div.
-  var r = document.createRange();
-  r.setStart(div.firstChild, 0);
-  r.setEnd(div.firstChild, 9);
-  sel.addRange(r);
+  const div = document.getElementById("copySource");
+  getSelection().setBaseAndExtent(div.firstChild, 0, div.firstChild, "Copy this".length);
+  info(`Selected test: "${getSelection().getRangeAt(0).toString()}"`);
 
   function checkResult() {
     var iframe = document.querySelector("iframe");
@@ -66,20 +60,23 @@ SimpleTest.waitForFocus(function() {
 
   SimpleTest.waitForClipboard(
     aData => {
-      // XXX Oddly, specifying `r.toString()` causes timeout in headless mode.
-      info(`copied text: "${aData}"`);
-      return true;
+      if (aData.includes(`${getSelection().getRangeAt(0)?.toString()}`)) {
+        return true;
+      }
+      info(`Text in the clipboard: "${aData}"`);
+      return false;
     },
     function setup() {
-      synthesizeKey("C", {accelKey: true});
+      synthesizeKey("c", {accelKey: true});
     },
     function onSuccess() {
-      setTimeout(pasteQuote, 0);
+      SimpleTest.executeSoon(pasteQuote);
     },
     function onFailure() {
       SimpleTest.finish();
     },
-    "text/html"
+    // TODO: bug 1686012
+    SpecialPowers.isHeadless ? "text/unicode" : "text/html"
   );
 });
 

testing/specialpowers/content/SpecialPowersChild.jsm

@@ -712,6 +712,10 @@ class SpecialPowersChild extends JSWindowActorChild {
     return Cr;
   }
 
+  get isHeadless() {
+    return Cc["@mozilla.org/gfx/info;1"].getService(Ci.nsIGfxInfo).isHeadless;
+  }
+
   get addProfilerMarker() {
     return ChromeUtils.addProfilerMarker;
   }