Reland of place string::find(prefix) == 0 pattern with base::StartsWith().

chrome/browser/apps/guest_view/web_view_browsertest.cc

Index: chrome/browser/apps/guest_view/web_view_browsertest.cc
diff --git a/chrome/browser/apps/guest_view/web_view_browsertest.cc b/chrome/browser/apps/guest_view/web_view_browsertest.cc
index 5cd24d4cde654f215d2607f88e736b488591f8a7..f8f2f81348ef7136003d8377ac509ec84c8dcb67 100644
--- a/chrome/browser/apps/guest_view/web_view_browsertest.cc
+++ b/chrome/browser/apps/guest_view/web_view_browsertest.cc
@@ -2355,7 +2355,8 @@
 std::unique_ptr<net::test_server::HttpResponse> HandleDownloadRequestWithCookie(
     std::queue<net::HttpStatusCode>* status_codes,
     const net::test_server::HttpRequest& request) {
-  if (request.relative_url.find(kDownloadPathPrefix) != 0) {
+  if (!base::StartsWith(request.relative_url, kDownloadPathPrefix,
+                        base::CompareCase::SENSITIVE)) {
     return std::unique_ptr<net::test_server::HttpResponse>();
   }