Bug 1008573 - Simplify D3D10 invalid region before we clear the surface. r=Bas

gfx/layers/d3d10/ThebesLayerD3D10.cpp

@@ -404,6 +404,8 @@ ThebesLayerD3D10::DrawRegion(nsIntRegion &aRegion, SurfaceMode aMode)
     return;
   }
 
+  aRegion.SimplifyOutwardByArea(100 * 100);
+
   nsRefPtr<gfxASurface> destinationSurface;
   
   if (aMode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
@@ -412,8 +414,6 @@ ThebesLayerD3D10::DrawRegion(nsIntRegion &aRegion, SurfaceMode aMode)
     destinationSurface = mD2DSurface;
   }
 
-  aRegion.SimplifyOutwardByArea(100 * 100);
-
   MOZ_ASSERT(mDrawTarget);
   nsRefPtr<gfxContext> context = new gfxContext(mDrawTarget);