Add one-time randomization support for FieldTrial, and the ability to

base/rand_util.h

Index: base/rand_util.h
diff --git a/base/rand_util.h b/base/rand_util.h
index a4ea479e334edad7d181e5b4e27da46744deed11..d678aa6de5e69e465697d3f255f306983098a87f 100644
--- a/base/rand_util.h
+++ b/base/rand_util.h
@@ -27,6 +27,10 @@ BASE_API uint64 RandGenerator(uint64 max);
 // Returns a random double in range [0, 1). Thread-safe.
 BASE_API double RandDouble();
 
+// Given input |bits|, convert with maximum precision to a rand-like
+// double, i.e. in the range [0, 1). Thread-safe.
+BASE_API double BitsToRandLikeDouble(uint64 bits);
+
 }  // namespace base
 
 #endif  // BASE_RAND_UTIL_H_