TextEditor: get CompletionAssistProvider from editor.

And not from the global object pool. This way, the editors that have
different highlighters for various language dialects, or editors that
support multiple languages in a single editor, can decide themselves on
what CompletionAssistProvider to provide.

Change-Id: Ieebc4a8e7b3de6470fdb8103035aa3b8b2ba6598
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -907,6 +907,13 @@ CppCompletionSupport *CppModelManager::completionSupport(Core::IEditor *editor)
         return 0;
 }
 
+CppCompletionAssistProvider *CppModelManager::completionAssistProvider(Core::IEditor *editor) const
+{
+    Q_UNUSED(editor);
+
+    return m_completionAssistProvider;
+}
+
 void CppModelManager::setCppCompletionAssistProvider(CppCompletionAssistProvider *completionAssistProvider)
 {
     ExtensionSystem::PluginManager::removeObject(m_completionAssistProvider);