Add a browser test for the chrome://site-engagement WebUI.

chrome/browser/ui/webui/engagement/site_engagement_ui_browsertest.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/strings/string_util.h"
+#include "chrome/browser/engagement/site_engagement_service.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
+#include "chrome/browser/ui/webui/chrome_web_ui_controller_factory.h"
+#include "chrome/common/url_constants.h"
+#include "chrome/test/base/in_process_browser_test.h"
+#include "chrome/test/base/ui_test_utils.h"
+#include "content/public/browser/child_process_security_policy.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/common/content_switches.h"
+#include "content/public/test/browser_test_utils.h"
+
+namespace {
+
+const GURL kExampleUrl = GURL("https://www.example.com/");
+
+}  // namespace
+
+class SiteEngagementUiBrowserTest : public InProcessBrowserTest {
+ protected:
+  // Returns the SiteEngagementService for the test browser profile.
+  SiteEngagementService* engagement_service() {
+    return SiteEngagementService::Get(browser()->profile());
+  }
+
+  // (Re)sets the base score for a URL's site engagement.
+  void ResetBaseScore(const GURL& url, double score) {
+    engagement_service()->ResetBaseScoreForURL(url, score);
+  }
+  void ResetBaseScoreToMax(const GURL& url) {
+    ResetBaseScore(url, engagement_service()->GetMaxPoints());
+  }
+
+  // Navigates the tab to the site engagement WebUI.
+  void NavigateToWebUi() {
+    content::WebContents* web_contents =
+        browser()->tab_strip_model()->GetActiveWebContents();
+
+    const GURL web_ui_url(std::string(content::kChromeUIScheme) + "://" +

[Bernhard Bauer, 2017/03/31 13:05:00]

Can you use JoinString here as well? Just in terms of characters, saving two
`std::string()` calls might already be worth it...

[Wez, 2017/04/05 20:49:37]

Done.

+                          std::string(chrome::kChromeUISiteEngagementHost));
+    EXPECT_TRUE(ChromeWebUIControllerFactory::GetInstance()->UseWebUIForURL(
+        web_contents->GetBrowserContext(), web_ui_url));
+    ui_test_utils::NavigateToURL(browser(), web_ui_url);
+    EXPECT_TRUE(
+        content::ChildProcessSecurityPolicy::GetInstance()->HasWebUIBindings(
+            web_contents->GetRenderProcessHost()->GetID()));
+
+    EXPECT_TRUE(content::WaitForLoadStop(web_contents));
+  }
+
+  // Waits for the tab to be populated with site engagement data.
+  void WaitUntilPagePopulated() {
+    ASSERT_TRUE(content::ExecuteScriptAndExtractBool(
+        browser()->tab_strip_model()->GetActiveWebContents(),
+        "window.setPagePopulatedCallbackForTest(function() {"
+        "  window.domAutomationController.send(true);"

[calamity, 2017/04/03 04:38:52]

And then here:

window.waitForPagePopulated().then(() => {
  window.domAutomationController.send(true);
});

[Wez, 2017/04/05 20:49:37]

Done.

+        "});",
+        &page_is_populated_));
+
+    ASSERT_TRUE(page_is_populated_);
+  }
+
+  // Verifies that a row exists for the specified site URL.
+  void ExpectPageContainsUrl(const GURL& url) {
+    ASSERT_TRUE(page_is_populated_);
+
+    bool found_url = false;
+    ASSERT_TRUE(content::ExecuteScriptAndExtractBool(
+        browser()->tab_strip_model()->GetActiveWebContents(),
+        base::JoinString(
+            {"var origin_cells = "
+             "    Array.from(document.getElementsByClassName('origin-cell'));"
+             "window.domAutomationController.send(origin_cells.reduce("
+             "    function(found, element) {"
+             "      return found || (element.innerHTML == '",
+             url.spec(),
+             "');"
+             "    }, false));"},
+            ""),
+        &found_url));
+    EXPECT_TRUE(found_url);
+  }
+
+ private:
+  // True if the page contains site engagement data.
+  bool page_is_populated_ = false;
+};
+
+IN_PROC_BROWSER_TEST_F(SiteEngagementUiBrowserTest, Basic) {
+  ResetBaseScoreToMax(kExampleUrl);
+
+  NavigateToWebUi();
+  WaitUntilPagePopulated();
+
+  ExpectPageContainsUrl(kExampleUrl);
+}