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 541fd775ad3589c4c663374a80053a28545f2049..6bfbcb4896d087e1a144aaa19d40aa42321bcebf 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 double in
+// the range [0, 1). Thread-safe.
+BASE_API double BitsToOpenEndedUnitInterval(uint64 bits);
+
 // Fills |output_length| bytes of |output| with cryptographically strong random
 // data.
 BASE_API void RandBytes(void* output, size_t output_length);