Bug 748308 - Support insertParagraph and insertLineBreak per spec/Blink/WebKit; r=masayuki

Previously we supported insertParagraph as a synonym for formatBlock
"p", which is both useless and incompatible with all other browsers.
Edge's behavior doesn't look useful and looks redundant with insertHTML
(although it matches the name nicely, probably because they invented
the command).  Blink/WebKit treat it the same as hitting Enter, which is
useful for cross-browser testing until we get synthesizeKey() in wpt.

At the same time, I added insertLineBreak, which Blink/WebKit support
with the same functionality as pressing Shift-Enter.

The new event.html failures are spurious -- we used to pass by mistake
because we didn't support insertlinebreak at all.  insertlinebreak.html
has only new passes, no new failures, although it's not clear on the
diff.

MozReview-Commit-ID: 16oPcxXwGcj

dom/html/nsHTMLDocument.cpp

@@ -2938,7 +2938,8 @@ static const struct MidasCommand gMidasCommandTable[] = {
   { "unlink",        "cmd_removeLinks",     "", true,  false },
   { "insertorderedlist",   "cmd_ol",        "", true,  false },
   { "insertunorderedlist", "cmd_ul",        "", true,  false },
-  { "insertparagraph", "cmd_paragraphState", "p", true,  false },
+  { "insertparagraph", "cmd_insertParagraph", "", true,  false },
+  { "insertlinebreak", "cmd_insertLineBreak", "", true,  false },
   { "formatblock",   "cmd_paragraphState",  "", false, false },
   { "heading",       "cmd_paragraphState",  "", false, false },
   { "styleWithCSS",  "cmd_setDocumentUseCSS", "", false, true },