[ios] Added a CHECK to didCommitNavigation: to debug crbug.com/676340.

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index 9862aab3701fc9ce38c96ee4e17a1f0fe3c8dc12..9a212d697014ceb269de4b82a58e84fc7c13b089 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -5239,6 +5239,15 @@ const NSTimeInterval kSnapshotOverlayTransition = 0.5;
 
 - (void)webView:(WKWebView*)webView
     didCommitNavigation:(WKNavigation*)navigation {
+  // This method will crash if |currentSessionEntry| is null. If this check is
+  // hit it means that |didStartProvisionalNavigation| was called as expected
+  // but it did not call |registerLoadRequest|. TODO(crbug.com/676721): remove
+  // this CHECK once there is at least one crash on this line (which means that
+  // |didStartProvisionalNavigation| did not call |registerLoadRequest| and it
+  // should be fixed.
+  CHECK([self currentSessionEntry] ||
+        ![_latestWKNavigation isEqual:navigation]);
+
   DCHECK_EQ(_webView, webView);
   _certVerificationErrors->Clear();