Add function to register a synthetic trial with the trial hash.

chrome/browser/metrics/chrome_metrics_service_accessor.h

Index: chrome/browser/metrics/chrome_metrics_service_accessor.h
===================================================================
--- chrome/browser/metrics/chrome_metrics_service_accessor.h	(revision 287382)
+++ chrome/browser/metrics/chrome_metrics_service_accessor.h	(working copy)
@@ -5,6 +5,9 @@
 #ifndef CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_
 #define CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_
 
+#include <stdint.h>
+#include <string>
+
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "chrome/browser/metrics/metrics_service_accessor.h"
@@ -46,6 +49,7 @@
   friend class extensions::MetricsPrivateGetIsCrashReportingEnabledFunction;
   friend class ::FlashDOMHandler;
   friend class system_logs::ChromeInternalLogSource;
+  friend class UmaSessionStats;
 
   FRIEND_TEST_ALL_PREFIXES(ChromeMetricsServiceAccessorTest,
                            MetricsReportingEnabled);
@@ -70,9 +74,15 @@
   // registered at a time for a given trial name. Only the last group name that
   // is registered for a given trial name will be recorded. The values passed
   // in must not correspond to any real field trial in the code.
-  static bool RegisterSyntheticFieldTrial(const std::string& trial,
-                                          const std::string& group);
+  static bool RegisterSyntheticFieldTrial(const std::string& trial_name,
+                                          const std::string& group_name);
 
+  // Same as RegisterSyntheticFieldTrial above, but takes a hash for the trial
+  // name, rather than computing it from the string.
+  static bool RegisterSyntheticFieldTrialWithNameHash(
+      uint32_t trial_name_hash,
+      const std::string& group_name);
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(ChromeMetricsServiceAccessor);
 };