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 36d5954076efa0bd05036b028b2e68f7f74314f4..43cbb9eb7603b80ec6ddd36c1e8c204a79bf2fda 100644
--- a/chrome/browser/policy/policy_browsertest.cc
+++ b/chrome/browser/policy/policy_browsertest.cc
@@ -2974,6 +2974,27 @@ 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