Bug 291789 part 3 - Try not to ever delete across table boundaries; r=ehsan

dom/imptests/failures/editing/conformancetest/test_runtest.html.json

@@ -376,12 +376,9 @@
   "[[\"delete\",\"\"]] \"<div style=white-space:pre-wrap>foo&nbsp; []bar</div>\" compare innerHTML":true,
   "[[\"delete\",\"\"]] \"<div style=white-space:pre-line>foo &nbsp;[]</div>\" compare innerHTML":true,
   "[[\"delete\",\"\"]] \"<div style=white-space:nowrap>foo &nbsp;[]</div>\" compare innerHTML":true,
-  "[[\"delete\",\"\"]] \"<p>foo<table><tr><td>bar</table><p>[]baz\" compare innerHTML":true,
   "[[\"delete\",\"\"]] \"foo<br><table><tr><td>[]bar</table>baz\" compare innerHTML":true,
-  "[[\"delete\",\"\"]] \"<p>foo<table><tr><td>bar<br></table><p>[]baz\" compare innerHTML":true,
   "[[\"delete\",\"\"]] \"<table><tr><td>foo<br><td>[]bar</table>\" compare innerHTML":true,
   "[[\"delete\",\"\"]] \"<table><tr><td>foo<br><tr><td>[]bar</table>\" compare innerHTML":true,
-  "[[\"delete\",\"\"]] \"<p>foo<table><tr><td>bar<br><br></table><p>[]baz\" compare innerHTML":true,
   "[[\"defaultparagraphseparator\",\"div\"],[\"delete\",\"\"]] \"foo<ol><li>[]bar<li>baz</ol>\": execCommand(\"defaultparagraphseparator\", false, \"div\") return value":true,
   "[[\"defaultparagraphseparator\",\"div\"],[\"delete\",\"\"]] \"foo<ol><li>[]bar<li>baz</ol>\" compare innerHTML":true,
   "[[\"defaultparagraphseparator\",\"div\"],[\"delete\",\"\"]] \"foo<ol><li>[]bar<li>baz</ol>\" queryCommandValue(\"defaultparagraphseparator\") before":true,

editor/libeditor/html/nsHTMLEditRules.cpp

@@ -2169,8 +2169,9 @@ nsHTMLEditRules::WillDeleteSelection(Selection* aSelection,
         return NS_OK;
       }
 
-      // don't cross table boundaries
+      // don't cross table boundaries -- cancel it
       if (InDifferentTableElements(leftNode, rightNode)) {
+        *aCancel = true;
         return NS_OK;
       }