Fix inconsistent FieldTrial group assignment due to float errors.

base/metrics/field_trial_unittest.cc

Index: base/metrics/field_trial_unittest.cc
===================================================================
--- base/metrics/field_trial_unittest.cc	(revision 222861)
+++ base/metrics/field_trial_unittest.cc	(working copy)
@@ -849,4 +849,20 @@
   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());
+  }
+}
+
 }  // namespace base