Make scrollbars in pinch viewport invisible until compositor makes them visible.

Source/core/frame/PinchViewport.cpp

Index: Source/core/frame/PinchViewport.cpp
diff --git a/Source/core/frame/PinchViewport.cpp b/Source/core/frame/PinchViewport.cpp
index ca2d0d8688441e3e7dbe6c2192cf859602751c7b..f8e5d750ed2618dcd4b73133bd67465b31d70bef 100644
--- a/Source/core/frame/PinchViewport.cpp
+++ b/Source/core/frame/PinchViewport.cpp
@@ -308,6 +308,11 @@ void PinchViewport::setupScrollbar(WebScrollbar::Orientation orientation)
         webScrollbarLayer = coordinator->createSolidColorScrollbarLayer(webcoreOrientation, thumbThickness, scrollbarMargin, false);
 
         webScrollbarLayer->setClipLayer(m_innerViewportContainerLayer->platformLayer());
+
+        // The compositor will control the scrollbar's visibility. Set to invisible by defualt
+        // so scrollbars don't show up in layout tests.
+        webScrollbarLayer->layer()->setOpacity(0);

[gmorrita, 2014/10/30 18:48:47]

Apparently having some API on WebScrollbarLayer looks better than touching
layer() directly?

+
         scrollbarGraphicsLayer->setContentsToPlatformLayer(webScrollbarLayer->layer());
         scrollbarGraphicsLayer->setDrawsContent(false);
     }