Correct iOS build for latest Xcode beta.

ios/net/request_tracker.mm

Index: ios/net/request_tracker.mm
diff --git a/ios/net/request_tracker.mm b/ios/net/request_tracker.mm
index 6eb21c3f7e231177b7b23987332a3e684a2bc8be..a4cfa5476e481550db23888c013e981630377bbd 100644
--- a/ios/net/request_tracker.mm
+++ b/ios/net/request_tracker.mm
@@ -34,7 +34,11 @@ class GlobalNetworkClientFactories {
   // Adds a factory.
   void AddFactory(CRNForwardingNetworkClientFactory* factory) {
     DCHECK(thread_checker_.CalledOnValidThread());
-    DCHECK_EQ(NSNotFound, [factories_ indexOfObject:factory]);
+    // TODO(justincohen): Cast indexOfObject to work around Xcode beta bugs.
+    // Revisit in future betas where hopefully these types match again.
+    // crbug.com/498825
+    DCHECK_EQ(NSNotFound,
+              static_cast<NSInteger>([factories_ indexOfObject:factory]));
     DCHECK(!IsSelectorOverriden(factory, @selector(clientHandlingRequest:)));
     DCHECK(!IsSelectorOverriden(factory,
                                 @selector(clientHandlingResponse:request:)));