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 4e902da2f356ea666098ca3d34b73518f418833a..23783c951daea0eac3d008b2fbde1219d6fe84c5 100644
--- a/base/rand_util.h
+++ b/base/rand_util.h
@@ -29,6 +29,10 @@ 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 BitsToOpenEndedUnitInterval(uint64 bits);
+
 // Returns a random string of the specified length.
 BASE_API std::string RandBytesAsString(size_t length);