Use multithreaded instead of apartment-threaded

Uses the multithreaded COM threading model in pdfium_test, instead of
the apartment-threaded one. Correct usage of the apartment-threaded
model requires a message pump, which console applications don't have.

The XPS object model service supports both threading models equally, so
the models are the same for us otherwise.

Bug: pdfium:2059
Change-Id: If6ecfea6199dd2877f93bd824b3ff988972aac4d
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/109250
Commit-Queue: K. Moon <kmoon@chromium.org>
Reviewed-by: Nigi <nigi@chromium.org>

samples/helpers/win32/com_factory.cc

diff --git a/samples/helpers/win32/com_factory.cc b/samples/helpers/win32/com_factory.cc
index 7da80a7..7c5fe44 100644
--- a/samples/helpers/win32/com_factory.cc
+++ b/samples/helpers/win32/com_factory.cc
@@ -25,8 +25,8 @@
 
 bool ComFactory::Initialize() {
   if (!initialized_) {
-    HRESULT result = CoInitializeEx(
-        nullptr, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);
+    HRESULT result =
+        CoInitializeEx(nullptr, COINIT_MULTITHREADED | COINIT_DISABLE_OLE1DDE);
     DCHECK_NE(RPC_E_CHANGED_MODE, result);
     initialized_ = SUCCEEDED(result);
   }