Add a policy to re-enable deprecated web platform features.

chrome/browser/policy/policy_browsertest.cc

Index: chrome/browser/policy/policy_browsertest.cc
diff --git a/chrome/browser/policy/policy_browsertest.cc b/chrome/browser/policy/policy_browsertest.cc
index 4eb055f90c03553500526eed164a1a182d7ea81a..ae9dfafb9cdfbe88ebd7346f73114e8cdd1a509c 100644
--- a/chrome/browser/policy/policy_browsertest.cc
+++ b/chrome/browser/policy/policy_browsertest.cc
@@ -2971,6 +2971,27 @@ IN_PROC_BROWSER_TEST_F(PolicyTest, NativeMessagingWhitelist) {
       prefs, "other.host.name"));
 }
 
+IN_PROC_BROWSER_TEST_F(PolicyTest,
+                       EnableDeprecatedWebPlatformFeatures_ShowModalDialog) {
+  base::ListValue enabled_features;
+  enabled_features.Append(base::Value::CreateStringValue("ShowModalDialog"));
+  PolicyMap policies;
+  policies.Set(key::kEnableDeprecatedWebPlatformFeatures,
+               POLICY_LEVEL_MANDATORY,
+               POLICY_SCOPE_USER,
+               enabled_features.DeepCopy(),
+               NULL);
+  UpdateProviderPolicy(policies);
+
+  ui_test_utils::NavigateToURL(browser(), GURL(content::kAboutBlankURL));
+  bool result = false;
+  EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      "domAutomationController.send(window.showModalDialog !== undefined);",
+      &result));
+  EXPECT_TRUE(result);
+}
+
 #endif  // !defined(CHROME_OS)
 
 }  // namespace policy