Don't allow link navigations for invalid URLs.

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 a1f5aa0211eef998ec0e47ebedb88e7325a85d75..4b3851642a5e02d492e6878998756f4ae43df959 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -4963,6 +4963,19 @@ - (void)webView:(WKWebView*)webView
   // retrieved state will be pending until |didCommitNavigation| callback.
   [self updatePendingNavigationInfoFromNavigationAction:action];
 
+  // Invalid URLs should not be loaded.  However, simply doing nothing upon
+  // tapping a link or button is a jarring user experience.  Instead, cancel
+  // the invalid navigation and load about:blank.
+  GURL requestURL = net::GURLWithNSURL(action.request.URL);
+  if (!requestURL.is_valid()) {
+    decisionHandler(WKNavigationActionPolicyCancel);
+    GURL aboutBlankURL(url::kAboutBlankURL);
+    web::NavigationManager::WebLoadParams loadParams(aboutBlankURL);
+    loadParams.referrer = [self currentReferrer];
+    self.webState->GetNavigationManager()->LoadURLWithParams(loadParams);
+    return;
+  }
+
   BOOL allowLoad = [self shouldAllowLoadWithNavigationAction:action];
 
   if (allowLoad) {