mandoline: Add back/forward support and UI.

mandoline/ui/phone_ui/phone_browser_application_delegate.cc

Index: mandoline/ui/phone_ui/phone_browser_application_delegate.cc
diff --git a/mandoline/ui/phone_ui/phone_browser_application_delegate.cc b/mandoline/ui/phone_ui/phone_browser_application_delegate.cc
index 1634382455576ba4cb8a1a91cf7480fdd22aa927..20e7af1451b3809c5e0ff021ee9d2d7ff924ce24 100644
--- a/mandoline/ui/phone_ui/phone_browser_application_delegate.cc
+++ b/mandoline/ui/phone_ui/phone_browser_application_delegate.cc
@@ -116,6 +116,12 @@ void PhoneBrowserApplicationDelegate::ProgressChanged(double progress) {
   // ...
 }
 
+
+void PhoneBrowserApplicationDelegate::BackForwardChanged(bool back_enabled,
+                                                         bool forward_enabled) {
+  // ...
+}
+
 void PhoneBrowserApplicationDelegate::TitleChanged(const mojo::String& title) {
   // ...
 }