Handle app custom icon via aura::Window property.

components/exo/shell_surface.cc

Index: components/exo/shell_surface.cc
diff --git a/components/exo/shell_surface.cc b/components/exo/shell_surface.cc
index a87a22af56e0276a7614d8091199e648e740e661..b22b47bc13951b28efac24fd2f4cb74e2ef8c858 100644
--- a/components/exo/shell_surface.cc
+++ b/components/exo/shell_surface.cc
@@ -492,6 +492,14 @@ void ShellSurface::SetTitle(const base::string16& title) {
     widget_->UpdateWindowTitle();
 }
 
+void ShellSurface::SetIcon(const gfx::ImageSkia& icon) {
+  TRACE_EVENT0("exo", "ShellSurface::SetIcon");
+
+  icon_ = icon;
+  if (widget_)
+    widget_->UpdateWindowIcon();
+}
+
 void ShellSurface::SetSystemModal(bool system_modal) {
   // System modal container is used by clients to implement client side
   // managed system modal dialogs using a single ShellSurface instance.
@@ -829,6 +837,10 @@ base::string16 ShellSurface::GetWindowTitle() const {
   return title_;
 }
 
+gfx::ImageSkia ShellSurface::GetWindowIcon() {
+  return icon_;
+}
+
 void ShellSurface::SaveWindowPlacement(const gfx::Rect& bounds,
                                        ui::WindowShowState show_state) {
   if (bounds_mode_ != BoundsMode::CLIENT)