mandoline: Add automatic tracing at mojo call sites.

components/pdf_viewer/pdf_viewer.cc

Index: components/pdf_viewer/pdf_viewer.cc
diff --git a/components/pdf_viewer/pdf_viewer.cc b/components/pdf_viewer/pdf_viewer.cc
index b340273cbb9a49423865db65b28624ef785f4c40..2accf51e8bc43cc921648c3302b18a69d8ab562a 100644
--- a/components/pdf_viewer/pdf_viewer.cc
+++ b/components/pdf_viewer/pdf_viewer.cc
@@ -35,6 +35,7 @@
 #include "mojo/public/c/gles2/gles2.h"
 #include "mojo/public/c/system/main.h"
 #include "mojo/public/cpp/bindings/binding.h"
+#include "mojo/services/tracing/public/cpp/tracing_impl.h"
 #include "third_party/pdfium/public/fpdf_ext.h"
 #include "third_party/pdfium/public/fpdfview.h"
 #include "ui/gfx/geometry/rect.h"
@@ -603,6 +604,10 @@ class PDFViewer : public mojo::ApplicationDelegate,
 
  private:
   // ApplicationDelegate:
+  void Initialize(mojo::ApplicationImpl* app) override {
+    tracing_.Initialize(app);
+  }
+
   bool ConfigureIncomingConnection(
       mojo::ApplicationConnection* connection) override {
     connection->AddService(this);
@@ -615,6 +620,8 @@ class PDFViewer : public mojo::ApplicationDelegate,
     new ContentHandlerImpl(request.Pass());
   }
 
+  mojo::TracingImpl tracing_;
+
   DISALLOW_COPY_AND_ASSIGN(PDFViewer);
 };
 }  // namespace