Fix DCHECK in debug build when navigating to an unknown chrome://theme/ URL.

chrome/browser/ui/webui/chrome_url_data_manager_browsertest.cc

Index: chrome/browser/ui/webui/chrome_url_data_manager_browsertest.cc
diff --git a/chrome/browser/ui/webui/chrome_url_data_manager_browsertest.cc b/chrome/browser/ui/webui/chrome_url_data_manager_browsertest.cc
index 78ffc3226fe4942b391eb4eca82d348e638988c2..40e50c5c4d5f93371991b70298b4c74ac8dd1be5 100644
--- a/chrome/browser/ui/webui/chrome_url_data_manager_browsertest.cc
+++ b/chrome/browser/ui/webui/chrome_url_data_manager_browsertest.cc
@@ -57,11 +57,24 @@ IN_PROC_BROWSER_TEST_F(ChromeURLDataManagerTest, 200) {
   EXPECT_EQ(200, observer.http_status_code());
 }
 
+// Makes sure browser does not crash when navigating to an unknown resource.
+IN_PROC_BROWSER_TEST_F(ChromeURLDataManagerTest, UnknownResource) {
+  // Known resource
+  ui_test_utils::NavigateToURL(
+      browser(), GURL("chrome://theme/IDR_SETTINGS_FAVICON"));
+
+  // Unknown resource
+  ui_test_utils::NavigateToURL(
+      browser(), GURL("chrome://theme/IDR_ASDFGHJKL"));
+}
+
 // Makes sure browser does not crash when the resource scale is very large.
-IN_PROC_BROWSER_TEST_F(ChromeURLDataManagerTest, ResourceScaleTest) {
+IN_PROC_BROWSER_TEST_F(ChromeURLDataManagerTest, LargeResourceScale) {
+  // Valid scale
   ui_test_utils::NavigateToURL(
       browser(), GURL("chrome://theme/IDR_SETTINGS_FAVICON@2x"));
 
+  // Unreasonably large scale
   ui_test_utils::NavigateToURL(
       browser(), GURL("chrome://theme/IDR_SETTINGS_FAVICON@99999x"));
 }