Fixed a crash with some HP printer drivers (when invoking PTGetPrintCapabilit...

printing/backend/win_helper.cc

Index: printing/backend/win_helper.cc
===================================================================
--- printing/backend/win_helper.cc	(revision 70422)
+++ printing/backend/win_helper.cc	(working copy)
@@ -175,4 +175,36 @@
   return g_close_provider_proc(provider);
 }
 
+ScopedXPSInitializer::ScopedXPSInitializer() : initialized_(false) {
+  if (XPSModule::Init()) {
+    // Calls to XPS APIs typically require the XPS provider to be opened with
+    // PTOpenProvider. PTOpenProvider calls CoInitializeEx with
+    // COINIT_MULTITHREADED. We have seen certain buggy HP printer driver DLLs
+    // that call CoInitializeEx with COINIT_APARTMENTTHREADED in the context of
+    // PTGetPrintCapabilities. This call fails but the printer driver calls
+    // CoUninitialize anyway. This results in the apartment being torn down too
+    // early and the msxml DLL being unloaded which in turn causes code in
+    // unidrvui.dll to have a dangling pointer to an XML document which causes a
+    // crash. To protect ourselves from such drivers we make sure we always have
+    // an extra CoInitialize (calls to CoInitialize/CoUninitialize are
+    // refcounted).
+    HRESULT coinit_ret = CoInitializeEx(NULL, COINIT_MULTITHREADED);
+    // If this succeeded we are done because the PTOpenProvider call will
+    // provide the extra refcount on the apartment. If it failed because someone
+    // already called CoInitializeEx with COINIT_APARTMENTTHREADED, we try
+    // the other model to provide the additional refcount (since we don't know
+    // which model buggy printer drivers will use).
+    if (coinit_ret == RPC_E_CHANGED_MODE)
+      coinit_ret = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
+    DCHECK(SUCCEEDED(coinit_ret));
+    initialized_ = true;
+  }
+}
+
+ScopedXPSInitializer::~ScopedXPSInitializer() {
+  if (initialized_)
+    CoUninitialize();
+  initialized_ = false;
+}
+
 }  // namespace printing