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>

src/tools/clangbackend/ipcsource/clangcompletecodejob.h

@@ -0,0 +1,53 @@
+/****************************************************************************
+**
+** 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.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "clangasyncjob.h"
+#include "clangtranslationunit.h"
+
+#include <clangbackendipc/codecompletion.h>
+
+namespace ClangBackEnd {
+
+struct CompleteCodeJobResult
+{
+    CodeCompletions completions;
+    CompletionCorrection correction = CompletionCorrection::NoCorrection;
+};
+
+class CompleteCodeJob : public AsyncJob<CompleteCodeJobResult>
+{
+public:
+    using AsyncResult = CompleteCodeJobResult;
+
+    bool prepareAsyncRun() override;
+    void finalizeAsyncRun() override;
+
+private:
+    TranslationUnit m_pinnedTranslationUnit;
+};
+
+} // namespace ClangBackEnd