Remove legacy StartsWithASCII function.

ios/chrome/app/safe_mode_util_unittest.cc

Index: ios/chrome/app/safe_mode_util_unittest.cc
diff --git a/ios/chrome/app/safe_mode_util_unittest.cc b/ios/chrome/app/safe_mode_util_unittest.cc
index 1c9de677511e7cb5377f920320e93f1fee8a5b4d..c5f1d5b6f5cceecc7c3242a6314e122b78e21360 100644
--- a/ios/chrome/app/safe_mode_util_unittest.cc
+++ b/ios/chrome/app/safe_mode_util_unittest.cc
@@ -27,7 +27,8 @@ TEST_F(SafeModeUtilTest, GetAllImages) {
   string lib_system_prefix("libSystem");
   for (size_t i = 0; i < images.size(); ++i) {
     string base_name = base::FilePath(images[i]).BaseName().value();
-    if (base::StartsWithASCII(base_name, lib_system_prefix, true)) {
+    if (base::StartsWith(base_name, lib_system_prefix,
+                         base::CompareCase::SENSITIVE)) {
       found_lib_system = true;
       break;
     }