Addresses the following findings of QTCREATORBUG-12030:
 * qtc.helgrind.plugintests.txt#2
 * qtc.helgrind.usingEditors1.txt#1

Helgrind report (truncated):

Possible data race during write of size 4 at 0x23679618 by thread #1
Locks held: none
   at 0x6819003: ???
   by 0x681D713: ???
   by 0x68200DE: ???
   by 0x684B8F8: QTextCursor::insertText(QString const&, QTextCharFormat const&)
   by 0x684BCB9: QTextCursor::insertText(QString const&)
   by 0x139DA06C: TextEditor::BaseTextEditorWidget::keyPressEvent(QKeyEvent*) (basetexteditor.cpp:1866)
   by 0x184C999F: CppEditor::Internal::CPPEditorWidget::keyPressEvent(QKeyEvent*) (cppeditor.cpp:1416)

This conflicts with a previous read of size 4 by thread #18
Locks held: none
   at 0x680BC54: QTextDocument::revision() const
   by 0x159047F3: CppTools::CppEditorSupport::editorRevision() const (cpptoolseditorsupport.cpp:198)
   by 0x158E39BF: CppTools::Internal::CppModelManager::buildWorkingCopyList() (cppmodelmanager.cpp:525)
   by 0x158E3D5B: CppTools::Internal::CppModelManager::workingCopy() const (cppmodelmanager.cpp:544)
   by 0x1589FF6F: CppTools::Internal::CppCompletionAssistInterface::getCppSpecifics() const (cppcompletionassist.cpp:1957)
   by 0x158A1158: CppTools::Internal::CppCompletionAssistInterface::snapshot() const (cppcompletionassist.h:200)
   by 0x1589707C: CppTools::Internal::CppCompletionAssistProcessor::startCompletionInternal(QString, unsigned int, unsigned int, QString const&, int) (cppcompletionassist.cpp:1212)
   by 0x15893CC7: CppTools::Internal::CppCompletionAssistProcessor::startCompletionHelper() (cppcompletionassist.cpp:970)

---

Possible data race during write of size 4 at 0x24C8AD18 by thread #1


Locks held: none
   at 0x684AF23: QTextCursor::beginEditBlock()
   by 0x139D7D05: TextEditor::BaseTextEditorWidget::keyPressEvent(QKeyEvent*) (basetexteditor.cpp:1578)
   by 0x184C999F: CppEditor::Internal::CPPEditorWidget::keyPressEvent(QKeyEvent*) (cppeditor.cpp:1416)
   ...
   by 0x40F15A: main (main.cpp:533)

This conflicts with a previous read of size 4 by thread #11
Locks held: none
   at 0x680BC54: QTextDocument::revision() const
   by 0x159048D3: CppTools::CppEditorSupport::editorRevision() const (cpptoolseditorsupport.cpp:198)
   by 0x158E3A9F: CppTools::Internal::CppModelManager::buildWorkingCopyList() (cppmodelmanager.cpp:525)
   by 0x158E3E3B: CppTools::Internal::CppModelManager::workingCopy() const (cppmodelmanager.cpp:544)
   by 0x1590741E: parse(QFutureInterface<void>&, QSharedPointer<CppTools::SnapshotUpdater>) (cpptoolseditorsupport.cpp:299)

Task-number: QTCREATORBUG-12030
Change-Id: Idf0aa47f1f6bfd6814a961fe39d3b19b98f934f5
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>