Make SalInstance::CreateClipboard return a single instance in the non-LOK case

I came across this when seeing UITest_calc_tests2's
tdf118189.tdf118189.test_tdf118189 fail on Linux with SAL_USE_VCLPLUGIN=gen and
also on Windows, see the mailing list thread starting at
<https://lists.freedesktop.org/archives/libreoffice/2020-April/084822.html>
"Linux SAL_USE_VCLPLUGIN=svp and the clipboard".  That email thread clarified
that the codified behavior of that non-LOK test was wrong.  (While the LOK test
ScTiledRenderingTest::testMultiViewCopyPaste in
sc/qa/unit/tiledrendering/tiledrendering.cxx keeps working as intended.)

I did not find documentation for what arguments CreateClipboard shall support,
but things seem to work if anything but empty arguments is rejected with an
IllegalArgumentException.

Change-Id: I1918254cc15878ad43b8aa22aff7eb1c4bea73fe
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/91869
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sc/qa/uitest/calc_tests2/tdf118189.py

@@ -46,7 +46,7 @@ class tdf118189(UITestCase):
         self.xUITest.executeCommand(".uno:Undo")
 
         #-> CRASH
-        self.assertEqual(get_cell_by_position(document2, 0, 0, 0).getString(), "")
+        self.assertEqual(get_cell_by_position(document2, 0, 0, 0).getString(), "On Back Order")
 
         self.ui_test.close_doc()
 

vcl/inc/salinst.hxx

@@ -82,6 +82,7 @@ class VCL_DLLPUBLIC SalInstance
 private:
     rtl::Reference< vcl::DisplayConnectionDispatch > m_pEventInst;
     const std::unique_ptr<comphelper::SolarMutex> m_pYieldMutex;
+    css::uno::Reference<css::uno::XInterface> m_clipboard;
 
 public:
     SalInstance(std::unique_ptr<comphelper::SolarMutex> pMutex);

vcl/source/components/dtranscomp.cxx

@@ -17,14 +17,18 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
-#include <osl/mutex.hxx>
+#include <sal/config.h>
 
+#include <comphelper/lok.hxx>
+#include <osl/mutex.hxx>
+#include <tools/debug.hxx>
 #include <vcl/svapp.hxx>
 
 #include <factory.hxx>
 #include <svdata.hxx>
 #include <salinst.hxx>
 
+#include <com/sun/star/lang/IllegalArgumentException.hpp>
 #include <com/sun/star/lang/XMultiServiceFactory.hpp>
 #include <com/sun/star/lang/XServiceInfo.hpp>
 #include <com/sun/star/lang/XSingleServiceFactory.hpp>
@@ -452,9 +456,26 @@ Reference< XInterface > DropTarget_createInstance( const Reference< XMultiServic
 /*
 *   SalInstance generic
 */
-Reference< XInterface > SalInstance::CreateClipboard( const Sequence< Any >& )
+Reference< XInterface > SalInstance::CreateClipboard( const Sequence< Any >& arguments )
 {
-    return Reference< XInterface >( static_cast<cppu::OWeakObject *>(new vcl::GenericClipboard()) );
+    if (arguments.hasElements()) {
+        throw css::lang::IllegalArgumentException(
+            "non-empty SalInstance::CreateClipboard arguments", {}, -1);
+    }
+    if (comphelper::LibreOfficeKit::isActive()) {
+        // In LOK, each document view shall have its own clipboard instance, and the way that
+        // (happens to?) work is that apparently this function is called at most once for each such
+        // document view, so it is OK if we hand out a fresh instance on each call in LOK (whereas
+        // in non-LOK below we keep handing out one single instance; see also
+        // <https://lists.freedesktop.org/archives/libreoffice/2020-April/084824.html> "Re: Linux
+        // SAL_USE_VCLPLUGIN=svp and the clipboard"):
+        return Reference< XInterface >( static_cast<cppu::OWeakObject *>(new vcl::GenericClipboard()) );
+    }
+    DBG_TESTSOLARMUTEX();
+    if (!m_clipboard.is()) {
+        m_clipboard = static_cast<cppu::OWeakObject *>(new vcl::GenericClipboard());
+    }
+    return m_clipboard;
 }
 
 Reference< XInterface > SalInstance::CreateDragSource()