[UMA] Use proper C++ objects to serialize tracked_objects across process boundaries.

content/common/child_thread.h

Index: content/common/child_thread.h
diff --git a/content/common/child_thread.h b/content/common/child_thread.h
index a63e87c7e9af8541ddb4666ed51ca12a07ae073b..7941d5af4e3673808e2d3df9859bcacad49c1688 100644
--- a/content/common/child_thread.h
+++ b/content/common/child_thread.h
@@ -12,6 +12,7 @@
 #include "base/tracked_objects.h"
 #include "content/common/content_export.h"
 #include "content/common/message_router.h"
+#include "content/public/common/process_type.h"
 #include "webkit/glue/resource_loader_bridge.h"
 
 class FileSystemDispatcher;
@@ -101,7 +102,7 @@ class CONTENT_EXPORT ChildThread : public IPC::Channel::Listener,
 
   virtual void OnSetProfilerStatus(tracked_objects::ThreadData::Status status);
   virtual void OnGetChildProfilerData(int sequence_number,
-                                      const std::string& process_type);
+                                      content::ProcessType process_type);
 
   virtual void OnDumpHandles();