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 d89f8b725080d3912944b5b7bc60c19096c683ae..025c98589c6cd4deb0250a9ba763b69b7e0abb6a 100644
--- a/base/rand_util.cc
+++ b/base/rand_util.cc
@@ -23,6 +23,10 @@ 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
@@ -30,7 +34,7 @@ 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(result >= 0.0 && result < 1.0);
   return result;