Don't extend selection for special elements on caret based deletes

We should not extend selection looking for special elements if the
delete operation has been triggered by a caret based selection.

This change is based on a recent [1] resolution of the Editing TF,
which acknowledges that behavior of single-cell tables must be the
same that multi-cell tables and even if the last character is
deleted, we should not delete the whole table structure.

A different case would be when the user actively selects the whole
content of a table; in this case, as we do in multi-cell tables,
the structure of single-cell tables should be deleted together
with the content.

[1] w3c/editing#163

Bug: 731320
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I8c3e4efcc63410bf30b4889a715d92e9dda8189b
Reviewed-on: https://chromium-review.googlesource.com/1126255
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575591}

editing/data/delete.js

@@ -520,6 +520,11 @@ var browserTests = [
     "<div style=\"white-space:nowrap\">foo[]bar</div>",
     [true],
     {"delete":[false,false,"",false,false,""]}],
+["foo<table><tr><td>b[]</table>baz",
+    [["delete",""]],
+    "foo<table><tbody><tr><td>[]<br></td></tr></tbody></table>baz",
+    [true],
+    {"delete":[false,false,"",false,false,""]}],
 ["foo<table><tr><td>[]bar</table>baz",
     [["delete",""]],
     "foo<table><tbody><tr><td>[]bar</td></tr></tbody></table>baz",

editing/data/forwarddelete.js

@@ -215,6 +215,11 @@ var browserTests = [
     "foo{}",
     [true,true],
     {"defaultparagraphseparator":[false,false,"div",false,false,"p"],"forwarddelete":[false,false,"",false,false,""]}],
+["<table><tr><td>[]b</table>foo",
+    [["forwarddelete",""]],
+    "<table><tbody><tr><td>[]<br></td></tr></tbody></table>foo",
+    [true],
+    {"forwarddelete":[false,false,"",false,false,""]}],
 ["<table><tr><td>{}</table>foo",
     [["forwarddelete",""]],
     "<table><tbody><tr><td>{}</td></tr></tbody></table>foo",