Handle app custom icon via aura::Window property.

components/exo/shell_surface.h

Index: components/exo/shell_surface.h
diff --git a/components/exo/shell_surface.h b/components/exo/shell_surface.h
index 7443e48dc2d7696b23b2286d1a0335ac14381626..7ff115395708b4292bef5fb2ac49e8248f555f14 100644
--- a/components/exo/shell_surface.h
+++ b/components/exo/shell_surface.h
@@ -155,6 +155,9 @@ class ShellSurface : public SurfaceDelegate,
   // Set the application ID for the surface.
   void SetApplicationId(const std::string& application_id);
 
+  // Set icon for the window.
+  static void SetAppIcon(aura::Window* window, const gfx::ImageSkia& icon);
+
   // Start an interactive move of surface.
   void Move();
 
@@ -228,6 +231,7 @@ class ShellSurface : public SurfaceDelegate,
   bool CanMaximize() const override;
   bool CanMinimize() const override;
   base::string16 GetWindowTitle() const override;
+  gfx::ImageSkia GetWindowIcon() override;
   void SaveWindowPlacement(const gfx::Rect& bounds,
                            ui::WindowShowState show_state) override;
   bool GetSavedWindowPlacement(const views::Widget* widget,
@@ -378,6 +382,7 @@ class ShellSurface : public SurfaceDelegate,
   bool shadow_underlay_in_surface_ = true;
   bool pending_shadow_underlay_in_surface_ = true;
   bool system_modal_ = false;
+  gfx::ImageSkia icon_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellSurface);
 };