Use base::StartWith() in more places when appropriate.

components/nacl/renderer/ppb_nacl_private_impl.cc

Index: components/nacl/renderer/ppb_nacl_private_impl.cc
diff --git a/components/nacl/renderer/ppb_nacl_private_impl.cc b/components/nacl/renderer/ppb_nacl_private_impl.cc
index db128c400b8ec7c950096cd72bb3605bbecc96de..0d6eacf24793d2bf39ab67c6af163d4b654b16f4 100644
--- a/components/nacl/renderer/ppb_nacl_private_impl.cc
+++ b/components/nacl/renderer/ppb_nacl_private_impl.cc
@@ -1468,7 +1468,8 @@ void DownloadFile(PP_Instance instance,
 
   // Handle special PNaCl support files which are installed on the user's
   // machine.
-  if (url.find(kPNaClTranslatorBaseUrl, 0) == 0) {
+  if (base::StartsWith(url, kPNaClTranslatorBaseUrl,
+                       base::CompareCase::SENSITIVE)) {
     PP_NaClFileInfo file_info = kInvalidNaClFileInfo;
     PP_FileHandle handle = GetReadonlyPnaclFd(url.c_str(),
                                               false /* is_executable */,