Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

components/font_service/font_service_app.cc

Index: components/font_service/font_service_app.cc
diff --git a/components/font_service/font_service_app.cc b/components/font_service/font_service_app.cc
index b2c3297d7549667d105116e45c8c37e023b0f57d..7618296a4a197a6bdb8526e80df40b6bb9148191 100644
--- a/components/font_service/font_service_app.cc
+++ b/components/font_service/font_service_app.cc
@@ -58,8 +58,9 @@ FontServiceApp::FontServiceApp() {}
 
 FontServiceApp::~FontServiceApp() {}
 
-void FontServiceApp::Initialize(mojo::ApplicationImpl* app) {
-  tracing_.Initialize(app);
+void FontServiceApp::Initialize(mojo::Shell* shell, const std::string& url,
+                                uint32_t id) {
+  tracing_.Initialize(shell, url);
 }
 
 bool FontServiceApp::AcceptConnection(