Add/improve tracing in navigation.

content/browser/site_instance_impl.cc

Index: content/browser/site_instance_impl.cc
diff --git a/content/browser/site_instance_impl.cc b/content/browser/site_instance_impl.cc
index 6d5690d869d0319bac451718fd12ffac18164f26..987dd5c9d16693aea23add3c8b269ffe623054f8 100644
--- a/content/browser/site_instance_impl.cc
+++ b/content/browser/site_instance_impl.cc
@@ -120,6 +120,8 @@ RenderProcessHost* SiteInstanceImpl::GetProcess() {
                                                         process_, site_);
     }
 
+    TRACE_EVENT2("navigation", "SiteInstanceImpl::GetProcess",
+                 "site id", id_, "process id", process_->GetID());
     GetContentClient()->browser()->SiteInstanceGotProcess(this);
 
     if (has_site_)
@@ -131,6 +133,8 @@ RenderProcessHost* SiteInstanceImpl::GetProcess() {
 }
 
 void SiteInstanceImpl::SetSite(const GURL& url) {
+  TRACE_EVENT2("navigation", "SiteInstanceImpl::SetSite",
+               "site id", id_, "url", url.possibly_invalid_spec());
   // A SiteInstance's site should not change.
   // TODO(creis): When following links or script navigations, we can currently
   // render pages from other sites in this SiteInstance.  This will eventually