Add missing data members in StyleRareNonInheritedData copy constructor.

Two data members are missing from the StyleRareNonInheritedData copy
constructor. This can be problematic because StyleRareNonInheritedData
is stored with copy-on-write semantics: when two ComputedStyles share
the same StyleRareNonInheritedData, modifying one of them will create
a copy without copying those two data members.

This patch adds callback_selectors and paint_images into the copy
constructor.

BUG=628043

Review-Url: https://codereview.chromium.org/2893243002
Cr-Commit-Position: refs/heads/master@{#476577}
diff --git a/third_party/WebKit/Source/core/style/StyleRareNonInheritedData.cpp b/third_party/WebKit/Source/core/style/StyleRareNonInheritedData.cpp
index c5f5bec..327bb01b 100644
--- a/third_party/WebKit/Source/core/style/StyleRareNonInheritedData.cpp
+++ b/third_party/WebKit/Source/core/style/StyleRareNonInheritedData.cpp
@@ -176,6 +176,10 @@
       visited_link_border_right_color_(o.visited_link_border_right_color_),
       visited_link_border_top_color_(o.visited_link_border_top_color_),
       visited_link_border_bottom_color_(o.visited_link_border_bottom_color_),
+      callback_selectors_(o.callback_selectors_),
+      paint_images_(o.paint_images_
+                        ? new Vector<Persistent<StyleImage>>(*o.paint_images_)
+                        : nullptr),
       variables_(o.variables_ ? o.variables_->Clone() : nullptr),
       align_content_(o.align_content_),
       align_items_(o.align_items_),