Remove legacy StartsWithASCII function.

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 ef5e0daaefdda35a2bf2d616da5184fef1a76617..49bf49d40f776dc76b8cef075f99513403346562 100644
--- a/components/mime_util/mime_util.cc
+++ b/components/mime_util/mime_util.cc
@@ -161,10 +161,11 @@ bool MimeUtil::IsSupportedNonImageMimeType(const std::string& mime_type) const {
 #if !defined(OS_IOS)
          media::IsSupportedMediaMimeType(mime_type) ||
 #endif
-         (base::StartsWithASCII(mime_type, "text/",
-                                false /* case insensitive */) &&
+         (base::StartsWith(mime_type, "text/",
+                           base::CompareCase::INSENSITIVE_ASCII) &&
           !IsUnsupportedTextMimeType(mime_type)) ||
-         (base::StartsWithASCII(mime_type, "application/", false) &&
+         (base::StartsWith(mime_type, "application/",
+                           base::CompareCase::INSENSITIVE_ASCII) &&
           net::MatchesMimeType("application/*+json", mime_type));
 }
 
@@ -179,7 +180,8 @@ bool MimeUtil::IsSupportedJavascriptMimeType(
 }
 
 bool MimeUtil::IsSupportedMimeType(const std::string& mime_type) const {
-  return (base::StartsWithASCII(mime_type, "image/", false) &&
+  return (base::StartsWith(mime_type, "image/",
+                           base::CompareCase::INSENSITIVE_ASCII) &&
           IsSupportedImageMimeType(mime_type)) ||
          IsSupportedNonImageMimeType(mime_type);
 }