Fix loading success.html at the end of chrome://chrome-signin flow

This CL lists success.html as an webview accessible resource for
the sign-in extension.

This CL adds an exception for sign-in extension when for loading
webview accessible resources.

BUG=709117
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2831183003
Cr-Commit-Position: refs/heads/master@{#467739}

chrome/browser/ui/webui/signin/inline_login_ui_browsertest.cc

@@ -865,6 +865,33 @@ IN_PROC_BROWSER_TEST_F(InlineLoginUISafeIframeBrowserTest, NoWebUIInIframe) {
   ui_test_utils::NavigateToURL(browser(), url);
 }
 
+// Make sure that "success.html" can be loaded by chrome://chrome-signin.
+// http://crbug.com/709117
+IN_PROC_BROWSER_TEST_F(InlineLoginUISafeIframeBrowserTest,
+                       LoadSuccessContinueURL) {
+  ui_test_utils::NavigateToURL(browser(), GetSigninPromoURL());
+  WaitUntilUIReady(browser());
+
+  const std::string success_url =
+      GaiaUrls::GetInstance()->signin_completed_continue_url().spec();
+  const char* kLoadSuccessPageScript =
+      "var handler = function(e) {"
+      "  if (e.url == '%s') {"
+      "    window.domAutomationController.send('success_page_loaded');"
+      "  }"
+      "};"
+      "var extension_webview = inline.login.getAuthExtHost().webview_;"
+      "extension_webview.addEventListener('loadcommit', handler);"
+      "extension_webview.src = '%s';";
+  std::string script = base::StringPrintf(
+      kLoadSuccessPageScript, success_url.c_str(), success_url.c_str());
+
+  std::string message;
+  ASSERT_TRUE(content::ExecuteScriptAndExtractString(
+      browser()->tab_strip_model()->GetActiveWebContents(), script, &message));
+  EXPECT_EQ("success_page_loaded", message);
+}
+
 // Make sure that the gaia iframe cannot trigger top-frame navigation.
 // TODO(guohui): flaky on trybot crbug/364759.
 IN_PROC_BROWSER_TEST_F(InlineLoginUISafeIframeBrowserTest,

extensions/browser/url_request_util.cc

@@ -153,6 +153,22 @@ bool AllowCrossRendererResourceLoadHelper(bool is_guest,
                                           ui::PageTransition page_transition,
                                           bool* allowed) {
   if (is_guest) {
+    // Exceptionally, the resource at path "/success.html" that belongs to the
+    // sign-in extension (loaded by chrome://chrome-signin) is accessible to
+    // WebViews that are not owned by that extension.
+    // This exception is required as in order to mark the end of the the sign-in
+    // flow, Gaia redirects to the following continue URL:
+    // "chrome-extension://mfffpogegjflfpflabcdkioaeobkgjik/success.html".
+    //
+    // TODO(http://crbug.com/688565) Remove this check once the sign-in
+    // extension is deprecated and removed.
+    bool is_signin_extension =
+        extension && extension->id() == "mfffpogegjflfpflabcdkioaeobkgjik";
+    if (is_signin_extension && resource_path == "/success.html") {
+      *allowed = true;
+      return true;
+    }
+
     // An extension's resources should only be accessible to WebViews owned by
     // that extension.
     if (owner_extension != extension) {