Replace base::str[n]casecmp with helper functions.

components/mime_util/mime_util.cc

Index: components/mime_util/mime_util.cc
diff --git a/components/mime_util/mime_util.cc b/components/mime_util/mime_util.cc
index 3841fbbb69074cbadb8e513fb6b2334e06cf5b85..ef5e0daaefdda35a2bf2d616da5184fef1a76617 100644
--- a/components/mime_util/mime_util.cc
+++ b/components/mime_util/mime_util.cc
@@ -221,8 +221,8 @@ net::CertificateMimeType GetCertificateMimeTypeForMimeType(
   // Don't create a map, there is only one entry in the table,
   // except on Android.
   for (size_t i = 0; i < arraysize(kSupportedCertificateTypes); ++i) {
-    if (base::strcasecmp(mime_type.c_str(),
-                         kSupportedCertificateTypes[i].mime_type) == 0) {
+    if (base::EqualsCaseInsensitiveASCII(
+            mime_type, kSupportedCertificateTypes[i].mime_type)) {
       return kSupportedCertificateTypes[i].cert_type;
     }
   }