Fix inconsistent FieldTrial group assignment due to float errors.

base/metrics/field_trial_unittest.cc

 // Copyright (c) 2012 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.
 
 #include "base/metrics/field_trial.h"
 
 #include "base/message_loop/message_loop.h"
 #include "base/rand_util.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 831 matching lines @@
   const char kGroupName[] = "Group2";
   const int kProbability = 100;
   ASSERT_FALSE(FieldTrialList::TrialExists(kTrialName));
 
   FieldTrial* trial =
       CreateFieldTrial(kTrialName, kProbability, kDefaultGroupName, NULL);
   trial->AppendGroup(kGroupName, kProbability);
   EXPECT_EQ(kGroupName, trial->group_name());
 }
 
+TEST_F(FieldTrialTest, FloatBoundariesGiveEqualGroupSizes) {
+  const int kBucketCount = 100;
+
+  // Try each boundary value |i / 100.0| as the entropy value.
+  for (int i = 0; i < kBucketCount; ++i) {
+    const double entropy = i / static_cast<double>(kBucketCount);
+
+    scoped_refptr<base::FieldTrial> trial(
+        new base::FieldTrial("test", kBucketCount, "default", entropy));
+    for (int j = 0; j < kBucketCount; ++j)
+      trial->AppendGroup(base::StringPrintf("%d", j), 1);
+
+    EXPECT_EQ(base::StringPrintf("%d", i), trial->group_name());
+  }
+}
+
+TEST_F(FieldTrialTest, DoesNotSurpassTotalProbability) {
+  const double kEntropyValue = 1.0 - 1e-9;
+  ASSERT_LT(kEntropyValue, 1.0);
+
+  scoped_refptr<base::FieldTrial> trial(
+      new base::FieldTrial("test", 2, "default", kEntropyValue));
+  trial->AppendGroup("1", 1);
+  trial->AppendGroup("2", 1);
+
+  EXPECT_EQ("2", trial->group_name());
+}
+
 }  // namespace base