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"));

[mmenke, 2016/08/30 14:42:38]

optional:  Maybe run Javascript to make sure the page's text contains
ERR_FAILED?  Admittedly, seems unlikely this will ever not be an error page, but
I'm paranoid.

Would be something like:

  std::string command = base::StringPrintf(
      "var textContent = document.body.innerText;"
      "var hasText = textContent.indexOf('ERR_FAILED') >= 0;"
      "domAutomationController.send(hasText);");
  bool result = false;
  EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
      browser->tab_strip_model()->GetActiveWebContents(), command, &result));
  EXPECT_TRUE(result)

That does introduce a dependency on the error page displaying ERR_FAILED, of
course.

[Peter Kasting, 2016/08/30 19:46:07]

That's all true, but I think the more important question is whether we want this
to be testing that the specific result in this case is an error page of any
kind, and that the error code involved is ERR_FAILED.  I could see an argument
for doing this as a way of ensuring someone doesn't cause these requests to
erroneously succeed.  I could also see an argument that this is a bit of a
change detector test since we don't care how unknown resources are presented to
the user, just that they don't cause a crash.

I am on the fence.

+}
+
 // 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"));
 }