Bug 1582215 - Make `HTMLEditor::DoInsertHTMLWithContext()` compute new insertion point before removing unnecessary `<li>` elements r=m_kato

When inserting `<li>` elements into `<ul>`, `<ol>` or `<li>` element,
`HTMLEditor::DoInsertHTMLWithContext()` removes unnecessary empty `<li>`
elements at insertion point.  At this time, we've computed next insertion
point with removed `<li>` element.  Therefore, insertion point goes out
from the DOM tree.  This patch makes it compute new insertion point before
removing each empty `<li>` element.

Additionally, this patch adds some WPT data for testing this case.  I verified
that Chrome passes the new tests too.

Differential Revision: https://phabricator.services.mozilla.com/D49394

--HG--
extra : moz-landing-system : lando

editor/libeditor/HTMLEditorDataTransfer.cpp

@@ -495,9 +495,10 @@ nsresult HTMLEditor::DoInsertHTMLWithContext(
                   pointToInsert.GetContainer()->GetParentNode(),
                   "Insertion point is out of the DOM tree");
               if (pointToInsert.GetContainer()->GetParentNode()) {
-                DeleteNodeWithTransaction(
-                    MOZ_KnownLive(*pointToInsert.GetContainer()));
                 pointToInsert.Set(pointToInsert.GetContainer());
+                AutoEditorDOMPointChildInvalidator lockOffset(pointToInsert);
+                DeleteNodeWithTransaction(
+                    MOZ_KnownLive(*pointToInsert.GetChild()));
               }
             }
           }

testing/web-platform/tests/editing/data/inserthtml.js

@@ -360,6 +360,26 @@ var browserTests = [
     "<ul><li>f<ul><li>abc</li></ul>{}o</li></ul>",
     [true],
     {"inserthtml":[false,false,"",false,false,""]}],
+["<ul id=\"old\"><li id=\"li0\">{}<br></ul>",
+    [["inserthtml","<ul id=\"new\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ul>"]],
+    "<ul id=\"old\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ul>",
+    [true],
+    {"inserthtml":[false,false,"",false,false,""]}],
+["<ol id=\"old\"><li id=\"li0\">{}<br></ol>",
+    [["inserthtml","<ol id=\"new\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ol>"]],
+    "<ol id=\"old\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ol>",
+    [true],
+    {"inserthtml":[false,false,"",false,false,""]}],
+["<ul id=\"old\"><li id=\"li0\">{}<br></ul>",
+    [["inserthtml","<ol id=\"new\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ol>"]],
+    "<ul id=\"old\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ul>",
+    [true],
+    {"inserthtml":[false,false,"",false,false,""]}],
+["<ol id=\"old\"><li id=\"li0\">{}<br></ol>",
+    [["inserthtml","<ul id=\"new\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ul>"]],
+    "<ol id=\"old\"><li id=\"li1\">abc</li><li id=\"li2\">def</li></ol>",
+    [true],
+    {"inserthtml":[false,false,"",false,false,""]}],
 ["f[o]o",
     [["defaultparagraphseparator","div"],["inserthtml","<li>abc</li>"]],
     "f<div>abc</div>{}o",