Bug 1514940 - part 1: Forcibly disable new keyCode/charCode value of keypress events if the document is Confluence r=smaug,Ehsan,kmag

Old Confluence does not aware of conflated model keypress event (see UI Events
spec, https://w3c.github.io/uievents/#determine-keypress-keyCode).
Additionally, Confluence can be hosted with any domains.  Therefore, we cannot
use blacklist to disable the conflated model keypress event only on it.

This patch checks whether current or parent document is Confluence with JS
module, called KeyPressEventModelCheckerChild.  For kicking this module,
nsHTMLDocument dispatches an custom event, CheckKeyPressEventModel, when it
becomes editable only first time.  Finally, if it's a Confluence instance, the
module let PresShell know that we need to use split model keypress event in it.

Differential Revision: https://phabricator.services.mozilla.com/D17907

layout/base/PresShell.cpp

@@ -7811,7 +7811,7 @@ nsresult PresShell::EventHandler::DispatchEventToDOM(
             nsContentUtils::IsURIInPrefList(
                 uri,
                 "dom.keyboardevent.keypress.hack.dispatch_non_printable_keys");
-        mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues =
+        mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues |=
             nsContentUtils::IsURIInPrefList(uri,
                                             "dom.keyboardevent.keypress.hack."
                                             "use_legacy_keycode_and_charcode");