Add declaration for a newly defined highlight path property

A missing declaration broke some jumbo builds because in those
builds an implicit instantiation was seen before an explicit
specialization. This is illegal in C++. A forward declaration
solves the problem.

TBR=pbos@chromium.org,tapted@chromium.org

Bug: 861975,888204
Change-Id: Iecf736bcf9748d3c68265c21f9351c56d9a23dd8
Reviewed-on: https://chromium-review.googlesource.com/1245785Reviewed-by: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#594289}

ui/views/view_properties.h

@@ -47,5 +47,5 @@ VIEWS_EXPORT extern const ui::ClassProperty<gfx::Path*>* const
 DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(VIEWS_EXPORT, gfx::Insets*);
 DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(VIEWS_EXPORT,
                                         views::BubbleDialogDelegateView*);
-
+DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(VIEWS_EXPORT, gfx::Path*);
 #endif  // UI_VIEWS_VIEW_PROPERTIES_H_