Direct2D QPA: Never queue more than one frame

Microsoft recommends setting the maximum frame latency to 1:

http://blogs.windows.com/windows/b/appbuilder/archive/2013/12/18/optimizing-directx-apps-for-low-latency-input-and-longer-battery-life.aspx
http://msdn.microsoft.com/en-us/library/windows/desktop/hh780339(v=vs.85).aspx

Apparently it slightly reduces power consumption and it also slightly
increases performance. So let's set it.

Change-Id: I8a540f1e54e83d6dc13f25564e10b751e202ce66
Reviewed-by: Risto Avila <risto.avila@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/platforms/direct2d/qwindowsdirect2dcontext.cpp

@@ -90,7 +90,7 @@ public:
             return false;
         }
 
-        ComPtr<IDXGIDevice> dxgiDevice;
+        ComPtr<IDXGIDevice1> dxgiDevice;
         ComPtr<IDXGIAdapter> dxgiAdapter;
 
         hr = d3dDevice.As(&dxgiDevice);
@@ -99,6 +99,9 @@ public:
             return false;
         }
 
+        // Ensure that DXGI doesn't queue more than one frame at a time.
+        dxgiDevice->SetMaximumFrameLatency(1);
+
         hr = dxgiDevice->GetAdapter(&dxgiAdapter);
         if (FAILED(hr)) {
             qWarning("%s: Failed to probe DXGI Device for parent DXGI Adapter: %#x", __FUNCTION__, hr);