Clang: Process distinct documents concurrently

Speed ups the typical use cases that can profit from this:
 * Change a header file and switch then to source file
 * Open documents one after the other (Follow Symbol)
 * Change documents visible in splits (e.g. by refactoring action)
 * Restore a session with multiple splits

Fixes the test ClangIpcServer.GetCodeCompletionDependingOnArgumets.

Change-Id: Ia575bd59780df14146dfc091a4d48794e4a0543d
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

tests/unit/unittest/testutils.cpp

@@ -0,0 +1,54 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "testutils.h"
+
+#include <QCoreApplication>
+#include <QThread>
+#include <QTime>
+
+#include <QDebug>
+
+bool TestUtils::processEventsUntilTrue(std::function<bool ()> condition, int timeOutInMs)
+{
+    if (condition())
+        return true;
+
+    QTime time;
+    time.start();
+
+    forever {
+        if (condition())
+            return true;
+
+        if (time.elapsed() > timeOutInMs) {
+            qWarning() << "Timeout of" << timeOutInMs
+                       << "reached in processEventsAndWaitUntilTrue()";
+            return false;
+        }
+
+        QCoreApplication::processEvents();
+    }
+}