D17335: Install message handler after QApplication

[Kai Uwe Broulik]

broulik created this revision.
broulik added reviewers: Plasma, davidedmundson, fvogt.
Herald added a project: Plasma.
Herald added a subscriber: plasma-devel.
broulik requested review of this revision.

REVISION SUMMARY
  When using `qDebug` et all we will use `Connection::self()->sendMessage` to forward that to the browser. `Connection` uses a `QSocketNotifier` to listen to browser commands. This requires a working event dispatcher.
  
  When someone uses `qDebug` before `QApplication` initialized, e.g. `qt5ct` does this, our `QSocketNotifier` is defunct and we never receive any commands from the browser, breaking the extension.
  
  While `stdout` is reserved for communcation with the browser, where any random debug output will have the browser shut us down, `qDebug` prints on `stderr` which can be used for printing debug output, so no file descriptors are closed.
  
  BUG: 400906

TEST PLAN
  Installed qt5ct, `export QT_QPA_PLATFORMTHEME=qt5ct`, both Chromium and Firefox now show working media controls

REPOSITORY
  R856 Plasma Browser Integration

REVISION DETAIL
  https://phabricator.kde.org/D17335

AFFECTED FILES
  host/main.cpp

To: broulik, #plasma, davidedmundson, fvogt
Cc: plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart
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