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

base/rand_util.cc

Index: base/rand_util.cc
diff --git a/base/rand_util.cc b/base/rand_util.cc
index fc41ce8b4e9a6505ad816ae7faa32dfe726fd14d..4140e9a539867026e856f50e670118378f2512ea 100644
--- a/base/rand_util.cc
+++ b/base/rand_util.cc
@@ -25,6 +25,10 @@ int RandInt(int min, int max) {
 }
 
 double RandDouble() {
+  return BitsToOpenEndedUnitInterval(base::RandUint64());
+}
+
+double BitsToOpenEndedUnitInterval(uint64 bits) {
   // We try to get maximum precision by masking out as many bits as will fit
   // in the target type's mantissa, and raising it to an appropriate power to
   // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
@@ -32,7 +36,7 @@ double RandDouble() {
 
   COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
   static const int kBits = std::numeric_limits<double>::digits;
-  uint64 random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
+  uint64 random_bits = bits & ((GG_UINT64_C(1) << kBits) - 1);
   double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
   DCHECK_GE(result, 0.0);
   DCHECK_LT(result, 1.0);