Convert remaining StringToLowerASCII to ToLowerASCII

mojo/shell/network_fetcher.cc

Index: mojo/shell/network_fetcher.cc
diff --git a/mojo/shell/network_fetcher.cc b/mojo/shell/network_fetcher.cc
index da403a3a93207e3a4ca51a4bf09c01d6f5a9b015..c520477faf7247cf78f06341c4b73360c9c60c9b 100644
--- a/mojo/shell/network_fetcher.cc
+++ b/mojo/shell/network_fetcher.cc
@@ -130,7 +130,7 @@ bool NetworkFetcher::ComputeAppId(const base::FilePath& path,
   ctx->Finish(string_as_array(&output), output.size());
   output = base::HexEncode(output.c_str(), output.size());
   // Using lowercase for compatiblity with sha256sum output.
-  *digest_string = base::StringToLowerASCII(output);
+  *digest_string = base::ToLowerASCII(output);
   return true;
 }