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 4a455f1bd9e2a29d3aae27c6b6d9911c7ea401ec..dd4e079684382b5f8baa371caa4da878b66223c7 100644
--- a/base/rand_util.cc
+++ b/base/rand_util.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -23,6 +23,10 @@ int RandInt(int min, int max) {
 }
 
 double RandDouble() {
+  return BitsToRandDouble(base::RandUint64());
+}
+
+double BitsToRandDouble(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;