Make IsSolidColor() a property on CC scrollbar layers.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index ffd48bffcd3dd098d7fd757450d0f119cb0c5075..3c694517eec5082706dd03b86d1e0b4e58b239e9 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1260,7 +1260,7 @@ gfx::SizeF LayerTreeHostImpl::VisibleViewportSize() const {
   // The clip layer should be used if non-overlay scrollbars may exist since
   // it adjusts for them.
   LayerImpl* clip_layer = active_tree_->RootClipLayer();
-  if (!Settings().solid_color_scrollbars && clip_layer &&
+  if (!settings().force_solid_color_scrollbars && clip_layer &&
       clip_layer->masks_to_bounds())
     dip_size = clip_layer->bounds();
 
@@ -1568,7 +1568,7 @@ bool LayerTreeHostImpl::DeferredInitialize(
     scoped_refptr<ContextProvider> offscreen_context_provider) {
   DCHECK(output_surface_->capabilities().deferred_gl_initialization);
   DCHECK(settings_.impl_side_painting);
-  DCHECK(settings_.solid_color_scrollbars);
+  DCHECK(settings_.force_solid_color_scrollbars);
   DCHECK(output_surface_->context3d());
 
   ReleaseTreeResources();