Disable pinch zoom viewport for non-compositor scaling

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index 8f32526fbc635f0ef6ac3375c45755e1b89b4618..0694984a22bbd4675a47d4bdeea118387578040f 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -1298,7 +1298,9 @@ bool LayerTreeHostImpl::scrollBy(const gfx::Point& viewportPoint,
         if (!layerImpl->scrollable())
             continue;
 
-        PinchZoomViewport* viewport = layerImpl == m_rootScrollLayerImpl ? &m_pinchZoomViewport : 0;
+        PinchZoomViewport* viewport = NULL;
+        if (m_settings.pageScalePinchZoomEnabled && layerImpl == m_rootScrollLayerImpl)
+            viewport = &m_pinchZoomViewport;
         gfx::Vector2dF appliedDelta;
         if (m_scrollDeltaIsInViewportSpace) {
             float scaleFromViewportToScreenSpace = m_deviceScaleFactor;