Converted LayerImpl::bounds() to return SizeF.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 948c2bae3204342669eec1748c24ff0e0bdabd5f..6733919006d39cf7ec73a924d45c84e292e1a3e7 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -570,12 +570,12 @@ const LayerImplList& LayerTreeImpl::RenderSurfaceLayerList() const {
   return render_surface_layer_list_;
 }
 
-gfx::Size LayerTreeImpl::ScrollableSize() const {
+gfx::SizeF LayerTreeImpl::ScrollableSize() const {
   LayerImpl* root_scroll_layer = OuterViewportScrollLayer()
                                      ? OuterViewportScrollLayer()
                                      : InnerViewportScrollLayer();
   if (!root_scroll_layer || root_scroll_layer->children().empty())
-    return gfx::Size();
+    return gfx::SizeF();
   return root_scroll_layer->children()[0]->bounds();
 }