Fix more disabled MSVC warnings, base/ edition.

base/metrics/field_trial_unittest.cc

Index: base/metrics/field_trial_unittest.cc
diff --git a/base/metrics/field_trial_unittest.cc b/base/metrics/field_trial_unittest.cc
index a6dee1132c5b65bf914685dc0c9be39d14037eed..581803378eb99e15846526692ff77b6150b017f5 100644
--- a/base/metrics/field_trial_unittest.cc
+++ b/base/metrics/field_trial_unittest.cc
@@ -112,7 +112,7 @@ TEST_F(FieldTrialTest, AbsoluteProbabilities) {
   char default_always_true[] = " default always true";
   char always_false[] = " always false";
   char default_always_false[] = " default always false";
-  for (int i = 1; i < 250; ++i) {
+  for (char i = 1; i < 250; ++i) {
     // Try lots of names, by changing the first character of the name.
     always_true[0] = i;
     default_always_true[0] = i;
@@ -189,7 +189,7 @@ TEST_F(FieldTrialTest, MiddleProbabilities) {
   char default_group_name[] = " default same name";
   bool false_event_seen = false;
   bool true_event_seen = false;
-  for (int i = 1; i < 250; ++i) {
+  for (char i = 1; i < 250; ++i) {
     name[0] = i;
     default_group_name[0] = i;
     scoped_refptr<FieldTrial> trial =