Bug 1222943 (part 2) - Remove an unnecessary call to ToUnknownSize(). r=botond.

--HG--
extra : rebase_source : 8b6067d9e5897cd61a0752d9b665f1ebd9706df2

dom/ipc/TabParent.cpp

@@ -957,7 +957,7 @@ TabParent::UpdateDimensions(const nsIntRect& rect, const ScreenIntSize& size)
       ViewAs<LayoutDevicePixel>(mRect,
                                 PixelCastJustification::LayoutDeviceIsScreenForTabDims);
     LayoutDeviceIntSize devicePixelSize =
-      ViewAs<LayoutDevicePixel>(mDimensions.ToUnknownSize(),
+      ViewAs<LayoutDevicePixel>(mDimensions,
                                 PixelCastJustification::LayoutDeviceIsScreenForTabDims);
 
     CSSRect unscaledRect = devicePixelRect / widgetScale;