Bug 1258094 - Use SurfaceFormat::B8G8R8A8 as back buffer surface r=jrmuizel

widget/nsBaseWidget.cpp

@@ -1365,7 +1365,7 @@ nsBaseWidget::CreateBackBufferDrawTarget(mozilla::gfx::DrawTarget* aScreenTarget
                                          const LayoutDeviceIntRect& aRect)
 {
   MOZ_ASSERT(aScreenTarget);
-  gfx::SurfaceFormat format = aScreenTarget->GetFormat() == gfx::SurfaceFormat::B8G8R8X8 ? gfx::SurfaceFormat::B8G8R8X8 : gfx::SurfaceFormat::B8G8R8A8;
+  gfx::SurfaceFormat format = gfx::SurfaceFormat::B8G8R8A8;
   return aScreenTarget->CreateSimilarDrawTarget(aRect.ToUnknownRect().Size(), format);
 }