Add default argument to GetLocationBarSecurityIconTypeForSecurityState.

GetLocationBarSecurityIconTypeForSecurityState is called in downstream
test without passing should_downgrade flag. This is the follow up
change for crrev.com/c/1884428 which broke that test compilation.

Bug: 1020670
Change-Id: If70880dad334f9485f54911d2bd46cf2e0eb2f6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895866Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711847}

ios/chrome/browser/ui/omnibox/omnibox_util.h

@@ -34,9 +34,11 @@ UIImage* GetLocationBarSecurityIcon(LocationBarSecurityIconType icon);
 // Converts the |security_level| to an appropriate security icon type. If
 // |should_downgrade| is true, the info icon should be downgraded to a
 // grey triangle for non-secure connections.
+// TODO(crbug.com/1020670): remove default argument for |should_downgrade|
+// after updating GetLocationBarSecurityIconTypeForSecurityState call.
 LocationBarSecurityIconType GetLocationBarSecurityIconTypeForSecurityState(
     security_state::SecurityLevel security_level,
-    bool should_downgrade);
+    bool should_downgrade = false);
 
 // Converts the |security_level| to an appropriate icon in "always template"
 // rendering mode. If |should_downgrade| is true, the info icon should be