Make TracingImpl take a Shell* and args, instead of an ApplicationImpl*.

services/dart/content_handler_app.cc

Index: services/dart/content_handler_app.cc
diff --git a/services/dart/content_handler_app.cc b/services/dart/content_handler_app.cc
index 5db8dac401656daa714e191a97b698aa944b5598..380cd9224e383425472e30e980f195b6c91fb7f0 100644
--- a/services/dart/content_handler_app.cc
+++ b/services/dart/content_handler_app.cc
@@ -132,9 +132,9 @@ bool DartContentHandlerApp::run_on_message_loop() const {
 
 void DartContentHandlerApp::Initialize(mojo::ApplicationImpl* app) {
   // Tracing of content handler and controller.
-  tracing_.Initialize(app);
+  tracing_.Initialize(app->shell(), &app->args());
   // Tracing of isolates and VM.
-  dart_tracing_.Initialize(app);
+  dart_tracing_.Initialize(app->shell());
 
   // TODO(qsr): This has no effect for now, as the tracing infrastructure
   // doesn't allow to trace anything before the tracing app connects to the