Remove legacy StartsWithASCII function.

mojo/runner/shell_apptest.cc

Index: mojo/runner/shell_apptest.cc
diff --git a/mojo/runner/shell_apptest.cc b/mojo/runner/shell_apptest.cc
index 2a943d6e7f006d5f00c917e5f3ec09952ec015ca..13ddf36e7b83397d4d4f2908887e366575bc9e3a 100644
--- a/mojo/runner/shell_apptest.cc
+++ b/mojo/runner/shell_apptest.cc
@@ -42,7 +42,8 @@ class GetHandler : public http_server::HttpHandler {
       http_server::HttpRequestPtr request,
       const Callback<void(http_server::HttpResponsePtr)>& callback) override {
     http_server::HttpResponsePtr response;
-    if (base::StartsWithASCII(request->relative_url, "/app", true)) {
+    if (base::StartsWith(request->relative_url, "/app",
+                         base::CompareCase::SENSITIVE)) {
       response = http_server::CreateHttpResponse(
           200, std::string(kPingable.data, kPingable.size));
       response->content_type = "application/octet-stream";