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(base::JoinString(
+        {content::kChromeUIScheme, "://", 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.pageIsPopulatedPromiseForTest().then(function() {"

[Bernhard Bauer, 2017/04/06 15:20:47]

Nit: I realize that technically the function does return a promise, but
calamity's suggestion of waitForPagePopulated() does read more intuitive. And I
would also use arrow notation for the function. (Potentially also in the JS
file; it's not super common yet in our WebUI code, but it's definitely allowed,
and it is more concise.)

[Wez, 2017/04/06 23:48:06]

Ah, I see your point; you want the call site to read naturally with the then()
syntax.  Calling the function whenPageIsPopulated() seems the most appropriate
naming; wait...() implies that the function itself won't return until the page
has been populated.

I'd prefer to keep ForTest() as the suffix, since this is not intended for
general use.

I've also added Promise to the var name, to better disambiguate it from the
getter - though perhaps we don't need the getter function at all, and can just
let the test grab the Promise var directly - WDYT?
Done, here and in the JS.

+        "  window.domAutomationController.send(true);"
+        "});",
+        &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);
+}