In the .mm files use the crashpad::implicit_cast .. explicitly.

util/net/http_transport_mac.mm

Index: util/net/http_transport_mac.mm
diff --git a/util/net/http_transport_mac.mm b/util/net/http_transport_mac.mm
index af523c69c1775815f4ca5947840f2edd071dbbfe..891c56db8aeba7deb16994e4265884922a7e451a 100644
--- a/util/net/http_transport_mac.mm
+++ b/util/net/http_transport_mac.mm
@@ -203,7 +203,7 @@ bool HTTPTransportMac::ExecuteSynchronously(std::string* response_body) {
     NSInteger http_status = [http_response statusCode];
     if (http_status != 200) {
       LOG(ERROR) << base::StringPrintf("HTTP status %ld",
-                                       implicit_cast<long>(http_status));
+                                       crashpad::implicit_cast<long>(http_status));
       return false;
     }