Add rappor::SampleString for consisntecy with domain+registry case

components/rappor/rappor_utils.h

Index: components/rappor/rappor_utils.h
diff --git a/components/rappor/rappor_utils.h b/components/rappor/rappor_utils.h
index 721fade36a63bc7f8a4d4f1e9949adf8f363b1f1..8e425665d8eb7109aa74cdf97c990115705e0152 100644
--- a/components/rappor/rappor_utils.h
+++ b/components/rappor/rappor_utils.h
@@ -7,12 +7,21 @@
 
 #include <string>
 
+#include "components/rappor/rappor_service.h"
+
 class GURL;
 
 namespace rappor {
 
 class RapporService;
 
+// Records a string to a Rappor metric.
+// If |rappor_service| is NULL, this call does nothing.
+void SampleString(RapporService* rappor_service,
+                  const std::string& metric,
+                  RapporType type,
+                  const std::string& sample);
+
 // Extract the domain and registry for a sample from a GURL.
 // For file:// urls this will just return "file://" and for other special
 // schemes like chrome-extension will return the scheme and host.